Peace, and Thought reads: "Refresh Action: Exhaust 2 heroes to draw 5 cards." Would it be possible to exhaust heroes not under your control? For example, in a 2-player game, exhausting one of your own heroes, and 1 of your partner's to fulfill this requirement?

This is covered in P.25 of the rulebook, under "Paying Costs":

Costs can only be payed with cards or resources that a
player controls. If an effect is canceled, the cost is still
considered to have been paid.

So you have to exhaust your heroes to pay the cost