Good question. In order to answer your question, it is important to carefully read the personal guaranty that your father signed as to its language and if it references a subsequent lease to be signed for a new period beyond the original lease. If it does and you have not signed the new lease, then the guaranty that your father recently signed does not obligate him on the future lease that has not been signed.I suggest that you and your father consult further with a landlord tenant attorney and bring all documents concerning the lease that you have written about for him or her to review.From what you have written, you are not obligated under the new lease since you have not signed it.