Can kaushik gotra girl marry with kaushik gotra boy?

Answer 1

Yes they can marry, but their shaasan (sub-gotra)should be different.

Answer 2

generally same gotra marriage is not allowed but as kaushik is a very big gotra so in case if boy and girl are of same gotra then maariage can be possible if the sashan(village name of the gran grand father) for both gotra are diffrent.