How to have co-signer sign loan document

[Frank Y.]

Hello, all. I have a borrower who is going to borrow for fix & flip property. He is the sole owner of LLC, but his credit is not the best. He offered to have his wife, who has good credit, to co-sign. Our loan document include Mortgage, Promissory Note, and Guarantee Agreement. Where do I need the co-signer to sign? On all of these loan doc, or just sign on a separate one page Co-sign agreement where the co-signer will promise take all the liabilities of the loan document, if the borrower default? Please advise. Many thanks.

Frank