I'm sorry to hear about your Mum 💐
This is quite difficult for me to answer because your belief system is completely different to mine.
However, trying to take that into account, I would tell your Dad that you won't go because you don't like large crowds. I'm unclear if the trip was for your, his or both of your benefits - but if he still wants to go, one of your brothers can go with him.
I presume your father is unable to cook for himself? I'd probably cook for him a couple of times a week and ensure he has left overs he can have the other days. He can clean up himself.
Tell your brothers that their private lives are not more important than yours any any additional help your father needs is down to them.
Then laugh. I'm sorry, but that's really ALL you can do when someone is offering you blessed water to get rid of Satan. Ignore the bleeting to your brothers (unless you fear for your safety - then involve the police).
I'm sorry, this must feel like a slap in the face after you've been looking after him so well, ungrateful old sod.