Baby shower shenanigans

My father and his wife are refusing to come to my baby shower because it’s being held at my grandmothers house (his step mom) who he hasn’t spoken to since she had gotten cancer. He says he can’t put his wife through that, (being at her house) and that it’s not fair for her.

Now keep in mind, my step mom WANTED this baby shower however, they wanted me to rent a hall in order to avoid having it at her house AND expected my MIL to pay for it because she was the one who originally convinced me to have a shower.

This has me so pissed off right now, part of me really wants to cut them off from having anything to do with my child. Am I wrong?