How much is the loan for ?
The issue of a fee being paid to a Director for signing a PG for their firm is nonsense so kill that for a start, it is opportunistic on the part of your co-directors.
I agree with you not wanting to sign a PG but if the business needs it and the directors don't have capital to inject then you have a tough decision to make, sign it or don't sign it but depending on how large the loan is, how long you are banking with the company bank etc you should try to negotiate this away and not make it a condition of loan approval, not always easy to do that.