How to say "学长，学姐，学弟，学妹" in English?
How to say someone who shares the same major as me but is senior / junior to me in English?
We have specific names in Chinese, but there aren't any specific names to call them in the English dictionary.
So, how do you call them?

Question

How to say "学长，学姐，学弟，学妹" in English?
How to say someone who shares the same major as me but is senior / junior to me in English?
We have specific names in Chinese, but there aren't any specific names to call them in the English dictionary. 
So, how do you call them?

Answer

We don't have these words in English. If you like, you can say:
senior schoolmate
junior schoolmate
But I don't suggest using these words at all. If you must describe someone then you don't compare him to yourself. You just say he is 1st year, 2nd year, etc.

Answer

You could also say something like "one of the first year bio-chem students" or "one of the graduating pre-med students".

Answer

You just said it. senior/junior/fresh/soph.