Aside from the evidence, this contract should be valid. If both parties hold a contract that the lender has not signed, the lender will sign it together with the borrower and the guarantor, and he himself will not deny the establishment of the contract. Then who can deny the establishment of the contract? This is just a flaw in the contract, which can prove the relationship between the loan and the guarantee contract, and there is no evidence to the contrary. If both the borrower and the guarantor claim that the contract is invalid, then why do you sign the contract and give it to the other party for safekeeping?

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.