Man. I sure feel for 'ya brother.
My ex took the cocker spaniel I'd had since late 2005. She left in 2017 and I'd never have seen him again were it not for him breaking out of the house, running away, and her lack of following through meant the chip was still in my name so when he got picked up and taken to a vet (severely dehydrated, tired, weak and overheated) they called me. They even brought him to me and I got to spend several hours with him again before she came and got him.
Newton died in February and even though the ex had him and I haven't seen him since he ran away and came back that one time summer of 2019, it was still just as hard were he right here. I miss that little hardheaded dog. That little nub of a tail wagged constantly for 14 years.
So I have my setter and my cat, and I totally get it, they're family.
I agree to not let him suffer if he's there. That's totally your call and I agree, don't beat yourself up over it. You love him, you'll do the right thing when the time comes.
Your brothers are hear for 'ya too.