OP, your sister is a truly nasty piece of work which you are seeing very clearly, perhaps for the first time.
In a fit of pure viciousness she has told him to remove every trace of himself from his home or she will bin it?
Wow!
MN is often a parallel universe to me, because that IS as ugly and as nasty as it gets.
I hope for her that he moves on successfully in his life and he neither forgives nor forgets this.
She is an absolute disgrace and it screams covert narcissism.
I have 4 young adults here up to the mid 20's and I have never heard the likes of this.
It's what I have come to learn though on MN, the ugly reality when parents put a partner first.
He lost his father and this is what he has been left with? A disgrace.
However unlucky that poor lad is to have lost a dad and have an awful example like that for a mother, he is truly blessed in you, your husband and family.
The long term impact of your kindness and generosity will be something he will carry for ever.
Keep your sister away from your family, she has shown herself to be pure poison, and not someone you should want around you all.
I mean this kindly because you are a very nice woman, but be very careful of her.
The stress she has inflicted on her son is so awful.
That she could do this to her own child means she is truly toxic, and just because you haven't realised that before now, doesn't mean its not true.
Don't force him to be in contact with her.
Respect that he may not feel safe around her and want distance.
Hard to believe he will not have seen this side to her before.