Cool idea though.
The scamming that happens to homebuyers is not even comparable to the risk in uploading docs to a website which promises they won't share user data with anyone. This is genuinely a pro buyer tool with no association with any 3rd party.
The tool has already helped many people negotiate and get a better deal on their mortgage. Please before judging understand that 70% of buyers overpay in their mortgage 1-3% in closing costs and bad rates. It's mind boggling how much lenders get away with profiting in junk fees from stressed out homebuyers.
Privacy concerns are real but the importance of that matter in your project is overestimated here by an absurd level.
What I read is not a constructive criticism and the suggestions laid down are not realistic nor business relevant at all. I feel like this is some sort of mass wishful thinking.
This isn't about privacy, it's a security concern. People's life savings are on the line here, and the information OP is requesting is enough to pull off very sophisticated social engineering attacks. It's entirely reasonable to ask what they're going to do with that information and how they're keeping it secured, and their reaction to the questions is entirely inappropriate for someone who's asking for this degree of trust.