What seems to have happened is she has pressured FIL by giving him this new information that her husband is basically disinheriting her and thus needs even more
Right. So, not that she has had the closest relationship with your FiL by far, he would know what's going her life and he simply WANTS to help her in HER time of need as she's been the one to help him, then?
How old is your SiL, by the way?
Your entire family going up to chat to FIL is tantamount to coercion btw
Quite. If your DH wanted to 'connect' with his father about their relationship, what better forum to do it than during a friendly, mob-handed discussion about the will and who gets what from a sick old man.
The more you post OP, the worse it all sounds. You seem to struggle to empathise with anyone else involved, and the story about your DH and FiL shifts a bit through the thread to be honest. Plus, while you've stopped reminding us that your SiL was an alcoholic, you're now repeatedly suggesting that everyone's on 'your side' and everyone thinks SiL is the wrong, so you must be right, eh?
I strongly suspect your SiL deserves every penny she gets.
Our whole family are coming at Christmas, we have said will definitely be talking to them about inheritance
Maybe you should all talk about something else? itsnotaboutthemoney