I'm so sorry that you're having to go through the many struggles you report with your children and family.
While I understand the situation that you related, I am prevented by standards of practice issues from commenting specifically on your situation, and there are also restrictions on professional activity through Internet communication in jurisdictions in which the psychologist is not specifically licensed to practice.
But let me offer some general thoughts.
My approach to addressing alienation processes is from a clinical-treatment perspective, not a forensic-custody perspective. My focus is on the children's symptoms involved with the parent-child conflict, which requires establishing a diagnosis to guide treatment. The children present with a fixed-false belief system regarding the abusive-inadequate nature of the targeted-Delta parent, and treatment efforts that alter the responses of the targeted-Delta parent toward the child do not alter the children's behavior toward that parent (i.e., the child's behavior is not under the "stimulus control" of the targeted-Delta parent).
Through the process of collecting information relative to making a treatment-related diagnosis, I sometimes come to the diagnosis of a Shared Psychotic (delusional) Disorder when that diagnosis is warranted by the symptoms meeting the diagnostic criteria, and once that diagnosis is made, treatment requires the separation of the secondary case (the child) from the "inducer" or primary case (the alienating-Beta parent) in order to effectively treat the child's induced ("imposed" DSM-IV TR) psychotic (delusional) disorder. So separation of the child (the secondary case) from the alienating-Beta parent (the primary case) is not custody related, it's treatment related.
If the Court decides not to accept the treatment recommendation for the child's separation from the alienating-Beta parent, and allows the child to remain in contact with the primary case ("the inducer" DSM-IV TR), then treatment of the dysfunctions in the child's relationship with the targeted-Delta parent that are a consequence of the child's psychotic disorder (i.e., the shared delusional disorder with the alienating-Beta parent) will likely be ineffective, and so continued treatment of the relationship dysfunctions between the child and the targeted-Delta parent become contra-indicated pursuant to Section 10.10 (Terminating Therapy) of the Ethics Code for the American Psychological Association which requires that "psychologists terminate therapy when it becomes reasonably clear that the client/patient... is not likely to benefit..." Other therapists may decide to treat the relationship of the child and targeted-Delta parent, but I will decline/terminate treatment pursuant to Section 10.10 of the APA Ethics Code and my treatment-related diagnosis.
As long as a child with a Shared Psychotic Disorder remains in relationship with the source-origin of the delusional belief system (i.e., the primary case; the alienating-Beta parent) there is simply no point in treating the relationship distortions between the child and the targeted-Delta parent that occur as a consequence of the child's reality distortions that emerge from the delusional belief system that the child shares with the alienating-Beta parent.
I'd refer you to a handout I have posted on my website that quotes from the DSM-IV TR diagnoses involved, with my highlighting of particularly relevant segments. Regarding the diagnoses, note that the definition of a "delusion" according to the National Institute of Health is "a false belief regarding the self or persons or objects outside the self that persists despite the facts." The belief that the targeted-Delta parent is somehow abusive-inadequate and the children somehow need protection from the targeted-Delta parent is the "false belief" that "persists despite the facts" (i.e., by definition of the NIH; a delusion).
Also note that the diagnosis for a Delusional Disorder (the diagnosis given to the alienating-Beta parent) specifically requires that the delusion be "non-bizarre" (i.e., something that conceivably could happen, such as emotional abuse or neglect of a child), and the persecutory type identifies that "(...someone to whom the person is close) is being malevolently treated in some way" meaning that a parent's false and persistent belief that the child is being "malevolently treated in some way" meets the criteria for a persecutory delusion.
Also of particular relevance regarding the Shared Psychotic Disorder diagnosis (the diagnosis given to the child) is that the DSM-IV TR states in two separate sentences that separation from the primary case will generally resolve the delusion in the secondary case (i.e., the child). This seemingly indicates the recommended approach to treatment.
So, when a forensic evaluation is scheduled to be conducted, the targeted-Delta parent may wish to provide the evaluator with the relevant diagnostic criteria and suggest that the evaluator may wish to consider the appropriateness of this set of diagnoses. The targeted-Delta parent may wish to consider making this request in writing in hopes that formally documenting the request might encourage the evaluator to respond to this request in the report itself.
If a child has a serious medical disorder, such as cancer, it is important to make an accurate diagnosis in order to treat the medical issue. A physician who missed a diagnosis of cancer and thereby allowed the cancer to progress without treatment would be of serious concern, and the missed diagnosis may represent a case of professional negligence, professional incompetence, or even malpractice which might be actionable with the relevant regulatory boards.
If the criteria for a Delusional Disorder (persecutory type) are met for the alienating-Beta parent and the child shares this false belief system in the inadequacy/abusive nature of the targeted-Delta parent - resulting in the rejection-abandonment of the targeted-Delta parent, then a professional diagnosis of a Shared Psychotic Disorder appears warranted based on the diagnostic criteria being met. The failure of a mental health professional to make the diagnosis of either the Delusional Disorder with the alienating-Beta parent when the criteria are met, or the Shared Psychotic Disorder for the child when the diagnostic criteria are met would be of serious professional concern.
In cases where alienation processes are at least potentially possible, and particularly when one parent requests a specific evaluation for the potential diagnoses of a Delusional Disorder, persecutory type and Shared Psychotic Disorder, in my view the evaluator at least has the professional obligation to document his or her consideration of these diagnoses and the evidence that is not consistent with these diagnoses that led the evaluator to reject them as diagnostic possibilities, if indeed the diagnoses were rejected.
If it was my report in similar circumstances, I might document the diagnostic issue in the following way:
"Mr. XYZ requested consideration of a diagnosis of a persecutory delusional disorder with his ex-wife, Ms. ABC, and the possibility of a Shared Psychotic Disorder involving the potential shared persecutory delusion of Ms. ABC and the child. Mr. XYZ suggested that it was the child's shared false belief in the abusive-inadequacy of Mr. XYZ as a parent that was resulting in the child's hostile rejection-abandonment of the relationship with Mr. XYZ. This diagnostic possibility was considered within this evaluation, and the following evidence seemingly supported the diagnosis of a persecutory false belief system with Ms. ABC..."
"However, the following evidence suggested that the reported false belief that Mr. XYZ was emotionally abusive-inadequate as a parent (had a reasonable foundation in fact, and so would not represent a false belief relative to a diagnosis of a delusion) (was available to change based on contrary evidence presented to Ms. ABC, and so did not meet diagnostic criteria for a delusion) (was not a belief system that was also shared by the child, and was not involved in the child's rejection of a relationship with Mr. XYZ so that it would not represent a diagnosis of a Shared Psychotic Disorder)...."
"Therefore, based on a consideration of the available evidence, a diagnosis for the child of a Shared Psychotic Disorder involving a shared false belief of the child with Ms. ABC in the abusive-inadequate nature of Mr. XYZ as a parent, that is resulting in the child's rejection-abandonment of a relationship with Mr. XYZ (appears warranted) (does not appear warranted) at this time."
While I am a clinical psychologist, not a forensic psychologist, and I don't do custody evaluations, it would seemingly be important in a child custody evaluation to identify DSM-IV TR Axis I psychiatric diagnoses in the parents when the disorders are present. And with regard to a possible presence of a persecutory delusion, repeated accusations, both formal and informal, of child abuse made by one parent toward the other which are not supported by the evidence should at least trigger an assessment by the evaluator of the potential for a persecutory delusional disorder that "someone to whom the person is close" (the child) is “being malevolently treated in some way." And if a persecutory delusional disorder is identified with one of the parents, then a diagnosis of a Shared Psychotic (delusional) Disorder should at least be considered and evaluated relative to the child's motivations for rejection-abandonment of the targeted-Delta parent.
Best wishes in resolving your difficult family situation.