Dan has given a good answer. I just wanted to add that if you have three older brothers, you can call all of them "my older brother" (and if you have three younger brothers, you can call all of them "my younger brother"). For example, if I say, "My younger brother Steven plays guitar," that doesn't necessarily mean that Stephen is my ONLY younger brother. It just means he's my brother and he's younger than me. In many cases, though, we would just say "my brother," regardless of how many brothers you have, or what their ages are. To be specific about which brother you mean, you can add a name ("my brother Stephen"). But as Dan says, if you really want to be specific about their ages, you'll need to say "oldest," "second oldest," and so on.

There aren't any specific terms. In the particular case of three siblings, the one who is not the oldest or the youngest is often called referred to as "the middle" or "in the middle." "I'm the middle of three." Or, "I'm the oldest, Rita is youngest, and Susie is in the middle." In the particular case where you have exactly one older sibling, you can say "my big brother" or "my big sister." Similarly, if you have exactly one younger sibling, you can call them "my little brother" or "my little sister." When it is more complicated than that, we just have to use ordinal numbers (oldest, second oldest, third oldest, etc.) or use refer to ages in years.

Thanks all

Puedes decir: mi hermano menor tiene 10 años Yo soy mayor que mi hermano 5 años El más pequeño de mis hermanos tiene 10 años Espero que me entiendas y te sirva la información

'in terms of age'/ 'in terms of how old they are'. 'straight'? Do you mean 'not homosexual'? I'm also not sure what you mean by your question. I think you need to give more details. All we usually use is 'older/younger' and 'brother/sister'.