I think... it is up to your FIL.... to decide.
He may also still be mourning and grieving.
ASK him, first. It is also out of respect... to him, as the Patriarch, of the family.
It is not up to your SIL.
To me.
Don't assume, FIL 'should' bring SIL along.
She is a grown up and has her own issues.
He should not have to cater to her, when he is mourning himself.
He has his own, life and his dear wife passed away.
DO NOT LET, your SIL's mountainous issues.... take away from your FIL, nor the family's Holiday events.
The FOCUS here, to me, is your FIL.
Speak to your Husband. That is his Dad.
He is the one, in which his Wife died.
He should not be, under the issues of your SIL.
Speak to your FIL.... about what HE wants to do for the holidays.
Since, it was his wife, that used to host this.
ASK him, first.
Don't assume or take over anything... until you have a nice conversation with him on it.
Don't let SIL to make this all messy and murky.
Due to her own selfish issues.
THEN, once you have spoken to your FIL about it... THEN, make plans or not.
THEN, you could just tell SIL, what those holiday plans are.
Because... it is NOT up, to her.
When my Dad died... my Mom was of course, very despondent. But an older sibling of mine would make such DRAMA! It was selfish.. because she'd then criticize my Mom, to her face... about what should have been/what she should do/how she should now act/and how, SHE thought things should be, now. BUT it is not up to her.. it is up to my MOM. She was my Dad's Wife. We were ALL mourning... BUT the point is: it is very selfish, to create drama about yourself, when your own Parent, is mourning. Yes, everyone was profoundly sad... but I always, made a point to go by my Mom's wishes, first. The last thing she needed, was to cater to or worry about or play referee... between siblings who created 'drama' after my Dad's death. For me: My Mom came first. I watched out for her.... and how she wanted to proceed, with any holidays or events.
It is out of respect... she is the Elder.