@bigbootsweather I am so sorry, you’re in an impossible situation, particularly if B is plausible when he speaks to the professionals. But you know any peace you get now by not telling the truth will come back in spades when B can’t cope and expects you to pick up his mess.
Can you be very factual - i.e. I do not believe DM can live independently or with carers because x,y,z . B has said that he will look after her in his hime but practically I am unsure that will be feasible as he is at work 5 days a week. I am prepared to do a,b,c but I cannot have DM live with me and I believe this would be unsafe because of x,y,z already stated.
I find copilot very good for shaping difficult conversations and it gives you some of the trigger words that social care etc. are looking for to ascertain if someone can remain at home.
Sorry if this is too simplistic, I know how horrendous it is when you’re in the middle of it.