tabeniikimasshou...

how do you tell the difference between ...shall i go eat .and shall we go eat...when you use the above phrase..???

You can usually tell from the context as the pronoun is not specified grammatically I think.

If memory serves me, there's actually a could of rarely used endings that can be stuck at the end of pronouns to indicate multiple people. I believe that watashi ta chi would be read as "we". However, these get mixed up with questions of gender and the like and are usually avoided in favor of providing enough information to allow understanding from context.