Tenant couples requested rider agreement to lease.

[Patrick Idowu]

Hi all, 

I have a tenant couple who moved in 4 months ago. They are requesting an addendum to their current lease because their relationship has changed. They were supposed to pay the rent jointly, as stated in the lease agreement. However, it appears they agreed to split the rent 50/50, and one of them is not meeting this agreement. They are now requesting an addendum stating that each person is responsible for their own rent, and payments are not mutually exclusive. Please advice on what to do. Much appreciated. Thank you.