Ok, is this a car loan or a home loan? Do both co-signers own this car, or home? The same principle applies, the owners must sign off any loan that encumbers their property, but co-borrowers who aren't owners don't have the same interest.
I am guessing that this is a loan on a mobile home and its is designated as a motor vehicle loan, correct? Is there really a "new agreement" or is the new higher balance and/or higher payments/interest rate just part of the default provisions of the original loan agreement?
For example, in some loan agreements there is a provision that when a loan goes into default for non-payment, the contract that allows for penalties and increased interest to be charged on the account until the default is cured.
I am not an attorney in UT. You should consult with an attorney to review the terms of the original loan, and any subsequent changes to the terms.