Mystery of Callan brothers

I've got two brothers of my great grandfather who I believe to be twins, yet I can't find anything to solve this mystery. Michael Joseph Callan has a baptism record on Irish Roots in which he was baptised in the Naas Roman Catholic Church on 29th August 1897 and was supposedly born the day before (the 28th August). However, no GRO index reference can be found of him. He doesn't appear in the 1901 or 1911 censuses. He has a brother, William Joseph Callan who doesn't have a baptism record on Irish Roots, but a GRO index reference can be found for his birth being registered in Naas in the same year and quarter of Michael's baptism. I ordered this birth certificate of William and it says he was born 25th August 1897...only 3 days before Michael???

One theory is that they were twins and Michael died before the census. However, I haven't been able to look for a death record of him.

Another theory is that they are the same person, and their name was actually Michael William Joseph Callan or William Michael Joseph Callan, and the priest didn't record the name of William on the baptism record. Or the priest wrote Michael instead of William on the baptism.

Their parents names were Nicholas Callan and Margaret/Maggie Cross.

Any help will be appreciated.

Thanks,

Martin