Learn the essential steps on how to add a cosigner to a lease to strengthen your rental agreement. My dad has agreed to cosign a lease with me but I am afraid my application will just be thrown out since I cannot provide a credit score or any proof of income.A guarantor is similar to a co-signer. A cosigner for an apartment takes on the financial responsibility for a lease. Learn how having a cosigner can help someone get approved for an apartment. Guarantors must have an individual gross monthly income that is equal to or greater than 4x the monthly rent. You can visit their website to fill out a form online and Leap will be your cosigner for you. Lawyer's Assistant: I understand that you no longer want to be responsible for the lease agreement you cosigned for your son's rental unit. Any "ground rules" are totally unenforceable. The probate court clerk will have a packet of information for you to use with all the forms to fill out to open a probate case for the deceased.