It may be challenging with a 620 credit score. It would suggest a local lender or credit union. These lenders have in-house programs that offer some flexibility. It is also a good idea to see if any Iowa Finance Authority (IFA) programs could be helpful to you. If you are looking to purchase in any of the smaller towns outside of the QCA the USDA Rural Development could be an option.
Another option is to contact Residential Mortgage Network in Coralville. Give Jessica a call at 319-354-7501 to see what suggestions she may have for you.
Does your fiance have a relationship with a credit union here in town? Sometimes credit unions and local lenders who have the ability to keep their loans in house can make exceptions to general credit score guidelines because they won't be selling your loan after closing. If that isn't an option give Christy Schnackel with Cherry Creek Mortgage in Bettendorf a call. She has been great with some of my other clients at looking over a credit report to make sure everything is reported correct and then giving advise on what could quickly bump up that score. Good luck.
Check with Wells Fargo they can do some FHA loans down to a 580 credit score with 10%a down payment Depending on the reason for the lower credit score. They may also be able to look at his credit report to make sure something on there that could possibly not be his which could boost his credit score 20-30 points quickly. Several lenders can do a FHA loan with 3 1/2% down payment and 600 middle score. So you are very close to being there!! Good luck!