I closed on our house about a month before Mr R and I married.
The down payment was mostly mine and the mortgage payment comes out of my income. Honestly, since we were going to marry anyway, it never occurred to me to do any kind of legal stuff. Plus, we had been living together for years already so our finances were co-mingled.
I would talk to a lawyer about YOUR loaned money to them but I’d leave the other part to them… unless, of course, they were asking for advice. In which case, I’d recommend a local lawyer.
ETA: I purposely closed on the house before the wedding because I have fantastic credit and he had basically no credit. We were going to get a much better rate with just my credit score.