Can you buy a house with BTC? Yes! All you need is a buyer with coins and a seller that will accept them. The value of the transaction is as of the date of the contract, when the coins change hands.
Ofc you can buy a house with bitcoin, I'm preety sure that i've seen a few websites that lets you buy a property with bitcoin but i'm not sure how it works without a proper escrow.
If the owner of the house is accepting bitcoin then it's the best thing otherwise you can explain him how bitcoin work show him a few websites that accepts bitcoin. Probably then he'll change his mind.