When you say two incomes I would assume you mean your wife's income as well as yours. If the Loan is going to be forgiven you will probably want to use just one to keep the payment lower. If the loan is not forgiven leave the payment the same but send in extra every month to knock it out. That way if your tight one month your not missing a sally payment and she doesn't send her brother (Government) after you.
Good Luck, David Kleinik