I would find it odd to meet half siblings called
Thomas and
Tamsin but I wouldn’t comment on it. I would assume the parents didn’t realise. My father in law had half siblings called
Thomas &
Thomasina after their father
Thomas.
I could compromise with
Leon &
Leo
Jay can be used to honour someone with a J name but I would be more inclined to look for another version of the name ie.
Jacqueline,
Jack or
John either
Jack or
Ian.
Don’t take criticism from someone you wouldn’t take advice from