Do several things. Sounds like you might know your credit situation in full, but if not, you should, and you shouldn't rely on someone else to do this. Google "free credit score" and pick one of the sites that will give you ALL 3 credit scores during their free trial period for their monitoring service. Then, presuming you don't want their monitoring service, you cancel during the trial period and owe nothing. Do this for both you and your fiance. This is the only way you can judge how good or bad your and your fiance's credit situation really is. If you pull your credit, there's no hit for the inquiry with any of the 3 agencies, but if someone else does, they count that as a credit inquiry, which only adds to a potential decrease in your scores, albeit small.
With that in hand, you should have a better handle on what reality is. Presuming your credit situation is not that good, say 650 FICO or less (average of the 3), then bite the bullet and wait until you can fix your credit situation. You'll get a lot of feedback that you can still get a loan with bad credit - doesn't that sound lucicrous? Don't be the "now" generation, and buy something just because you can, you'll get taken to the cleaners with high interest rates, and high fees. Then, you'll feel good until the new house emotion wears off, but the loan payments and high interest will stick to you like glue.
If you're serious about fixing your credit situation, then fix it, but don't go from the frying pan into the fire by lobbing on more debt.