
The story reads as totally normal. Not many men change their name that much but, “I want the same last name as my grandma who I love very much and not my second dad who I don’t talk to” feels right and good and maybe even sweet. The man’s a monster. This is fine.
It’s weird I said “men” here. In the US women usually change their names once and men never. But adoption and grandma and going by initials are all changes I’ve seen and understand.