I just finished reading your sitch. I have an IHS and he is dealing with MLC. I have, in the last year and a half, dealt with a “teenager” living in the other room. Definitely weird.
One thing stood out that your Son wondered if she had dementia, as she had forgotten him and his brother. I know it was driven by the fact she has ignored them lately, but I know early in my situation, H did not reach out to D25 while she was in grad school, he recently told her he wants a divorce, and he ignored our pets. I seriously thought before the initial BD almost 16 months ago, that I WAS dealing with him and dementia. Once the BD that forgetfulness left. I think his brain was trying to process so much he could not keep track. Once it came to a head, he was able to get back to his “normal brain”.
I am sorry you’re here. It does seem like you’re doing very well processing this. You’ve got this.