So sorry about your grandfather, Cheery, and my condolences to you and your family.

I find that strange, too, that two of the sons would let the nature of the ceremony itself stop them from paying their last respects to their father--or, for that matter, their bereaved mother. Just because your grandfather and grandmother were/are observant Catholics doesn't mean those sons have to be, and a funeral mass certainly doesn't require them to embrace Roman Catholicism. I've always been impressed with the low-key, ceremonial, non-intrusive nature of Catholic funerals. No preaching or proselytizing. Communion and kneeling are always completely optional, even for confirmed Catholics. Sounds like a convenient excuse to cop an attitude to me.