Exclusion of mother from EHCP and mess up by SENDco

My sister's son has autism (Asperger's) resulting in moderate learning difficulties. He attends a mainstream college (year 13) and follows an academic pathway based on his own learning style and needs. He is likely to need assisted living arrangements in the future such is he vulnerability. His cognitive ability does not match his chronological age.

Relevant background: His mum and dad are separated with shared care with the parents having a very challenging relationship. Just before my nephew turned 18 he was 'encouraged' to cut ties with his mother and through the courts the father was 'encouraged' to re-establish the relationship for the sake of his son. This did not happen, despite my sisters attempts to restart contact. As my nephew has some cognitive issues it is believed it is unlikely he will have made this decision himself but as a result he has not seen his mother for many months.

His EHCP meeting took place just after he turned 18 and my sister was not told it had happened until she received a letter 2 weeks after it took place inviting her to the meeting that had already happened! When my sister made contact with the college they told her they had made a mistake and would get back to her with information as to how the meeting had gone. They didn't so my sister made contact with the County Council advisory service who said they would look into what had happened.

One month later it appears as if there has been failing after failing and my sister is at her wits end and is still none the wiser as to how the EHCP meeting went. Her son's father is refusing the engage in any dialogue so that avenue has also been closed. The latest update from the college is that they have spoken to my nephew and have informed my sister that her own son has now decided that she can have access to paperwork from the EHCP but she is not to attend any future meetings. Again, this is a young man whose vulnerability could be very much manipulated for another adult's gain. It also appears that the decision to exclude my sister from the EHCP was a mistake but has now possibly been worded as it was my nephew's decision, to cover over the mistake the SENDco and college have made.

I am an 'impartial' sister who is attempting to see both my sister's point of view as well as my nephew's but am extremely concerned that, despite him now turning 18, he has been presented with decisions that his cognitive ability and reasoning would not necessarily be able to comprehend the longer term impact. The longer the 'estranged' period extends the harder it will be for my nephew to re-establish his connections with the other half of his family when factoring in how he forms relationships and trust. And adding in the additional 'adult issues' between his parents it leaves my sister with no information about his well-being or educational needs. My sisters has tried so many avenues (including the courts and mediation) to ensure she has information about my nephew but her ex-husband excludes her at every opportunity as a method of abuse.

I would welcome anyone's thoughts on this and any advice on steps forward would be much appreciated.