You are correct. There are no crypto police to confiscate your home as collateral. So, you have to do the whole deal in crypto. Without oracles, your only foundational tools are: wallets, time and sign-offs as inputs to smart contracts. Everything is built up from there.

Right now you can get a DeFi loan at places like changenow.io that don't even require you to sign in. You put up crypto collateral. When you pay back the loan with accumulated interest you get your collateral back. If your collateral drops in value to 50% of the loan amount, you lose it and are released from the loan.

You could pay for home that way. But, I wouldn't recommend it. Maybe there are more suitable options out there I'm unaware of. It's all definitely a work in progress :P