OP, the BF/FF issue is a red herring.
You are getting no support from your mother, and, it would seem, your husband.
Telephone your mother, and tell her that you will not be cooking for 12 on Easter Sunday. She will have to make other arrangements. Then telephone anyone one else she has invited, and let them know.
Practise saying things like this. "I'm sorry, I don't want to discuss it, but I will not be cooking a big family dinner on Easter Sunday. You will have to make other arrangements."
Then when people say, "oh, but Granny was looking forward to it, " you can respond by saying, "I'm sorry about that, but I am not well enough, and will not be able to cook a big family dinner on Easter Sunday. I will let Granny know, and she can make other arrangements."
Broken record.
Don't be bullied by these people.