A mathematical statement Is it technically correct to write "Let $A$ and $B$ be two sets"? or we should write "Let $A,B$ be sets"? Actually I am confused whether by mentioning "two" we are ruling out the possibility of $A=B$. Please suggest!

As a reader, one should not make assumptions about mathematical statements which have not been stated. Thus I feel that you are not losing anything by saying "Let $A$ and $B$ be two sets".
If you have any extra conditions which you feel are non trivial for the reader, then you should mention them.
