Only one of the two sellers signed a contract. Is this enforcable?

[Rick Im]

There was an investment property listed by one of the owners. I signed a purchase agreement with one of the two sellers (the other seller is his wife). For some reason, the wife wasn't available, so we both signed the contract with a plan to have his wife sign it later. Now the seller wants to increase the purchase price or back out. Without the signature of the other seller, is this contact still enforceable?