Heron , I'm assuming that your brother Sam and your step brother Sam had different surnames, so it was only the first name that was the same.
Also I think that most people could understand why step siblings had the same name, whereas it's very difficult to explain why siblings have the same name, without having to explain that one is adopted .
" this is my step brother, Samuel Jones "
" so you are Sam Smith and he's Samuel Jones ? "
" yes that's right, my mum married his dad when I was 11 and Samuel was 15"
" wow, was that confusing growing up ? "
" no we soon got used to it , he's Samuel / SJ and I'm always Sam "
" cool"
Most people don't mind telling people they are step siblings. It's very common and there's no stigma . No one ever asks kids why their parents got divorced / remarried .
Its different with adoption. It's not that common, people are often very nosey and ask inappropriate questions.
Then children concerned have a right to privacy. It's not fair to put them in a position where they have to tell everyone at school, Cubs, football as kids and then everyone who knows them both for the rest of their lives .
" This is my brother Sam Jones "
" Ha ha very funny "
" no seriously , he's my brother and we are both called Sam Jones "
" Okayyyy, I guess your parents really liked the name , huh"
< weird look >
" my parents adopted him when he was 4 " ( total breach of confidentiality by brother ) or
" I was adopted when I was 4" . Followed by
" so he's not you real brother then? "
" why didn't your parents want you? "
" What do you know about your real parents ? "
Etc etc for the next 75 years