Re: Naming children for dead siblings
The deceased older siblings, if my grandmother's family is anything to go by, would themselves have been named after relatives, living or dead. For instance, in her family the father, Robert, named his first son William; William named his first son Robert; who named his son William ... My grandmother never mentioned this; as far as I knew, she was the only girl, and her brothers were John William, Edward and Robert. Long after her death, I looked up her family in UK census records and found the family consisting of Robert (eldest) and John William. I was puzzled - Robert was the youngest of them all, I knew that - and checked the death records. Sure enough, Robert had been the eldest son and had died at the age of I think eleven. Can't recall. That left John William, Edward, my grandmother and the youngest son: another Robert, who was always known as Bob. No idea whether the original Robert had a nickname and if so, what it was. For the record, John William was known as Jack and Edward as Ted. Oh, and Robert had a son and named him William, but William's marriage was childless and there the tradition ended.
As for going to Heaven, surely in Heaven of all places that wouldn't be a problem. If they all ended up in Hell, there would certainly be opportunities for unpleasant name-calling etc. But one wouldn't plan for that. Anyway, when fewer names were in use than there are now, any family in Heaven would have numerous relatives of all ages named John and Mary. I'm sure they all coped, as they would have in life.
In South Africa, the tradition in Afrikaans families used to be very powerful: first son named after paternal grandfather, second son after maternal grandfather ... same for girls and grandmothers. Now, that would be a rarity. Fashions have changed, international trends have become acceptable rather than threatening, and parents are quite capable of splicing their own names together to make a new one, especially for girls: I know a Jeanine who married a Rudolf and named their daughter Runine, which I found unfortunate but they found meaningful.