Complicated Lease question

Hi everyone, I am new to avail and I have a question. My Tenant‘s brother took over the lease but the tenant actually wants the primary to be the brother and we still wanna keep the lease date April 30, 2027 so how would you set up the lease and make sure you’re getting the background and credit information and and the kicker is the brother works for the previous Tenant so there’s a lot of trust here but they’ve been long time renters with me for more than eight years at least the Tenant, but that doesn’t mean that the brother is going to be like that so I just want to do it all correct but there’s family involved and my Realtor didn’t want to do it because she said it will be a full payment of the first months rent since it’s not a full lease. Would love to hear your thoughts