question on preposition

Depends on what you mean. Is the exploring a future plan/intention? - ('to explore', or 'so as to explore'). Is it happening now, badly, and co-ordinating will improve the exploration? - ('in exploring')

in exploring is the correct verb-gerund combination, which shows that We and Peter are coordinating our efforts to jointly explore the business.

If you intend a slightly more distant meaning, then the remainder of the sentence needs to be revised as a relative clause: We need to coordinate with Peter, who is exploring...  The meaning is similar, but in my first suggested revision, the coordination aimed at exploring the potential business together sounds more collaborative; in the second, perhaps the coordination sounds less collaborative, suggesting that you will coordinate with Peter in other ways, but he will pursue the business potential more or less independently.

I hope this helps.

I spoke to her.............the office.