You don't have to go into forbearance if you want to pay interest only. SallieMae Medloans offer several payment plans - one is called "income sensetive repayment", which lets you choose to pay from 4%-25% of your income monthly towards your loans - you choose how much you want to budget to it. Of course, interest builds this way, but if you intent to pay something to your loans during residency anyway, this is a way to do it. Also there are several graduated repayment plans, starting low and building. Check out their website
www.salliemae.com to see the options they offer. Other lenders likely have the same deals.
When I went to get a mortgage, they just wanted letters from my lender saying that I could be eligible for deferrment, forbearance, etc., but they were very generic letters, not specific to my financial situation, but specific to the loan types I had out.
Don't forget, your income alone, not your spouse's income, is what counts towards deferrment eligibility. So don't worry about your spouse's income holding you back.