end of year lease. One staying, one leaving and one new tenant

[Martine Ayers]

I currently have 3 people on a year lease that is ending soon. The 2 original tenants have lived there for several years. Near the end of the first lease a 3rd tenant moved in. I did a background and credit check and when it came back good I added them to the lease thru an "additional tenant addendum". 2 of the tenants are moving out to buy a house together but the other one wants to stay. She found someone that wants to move in and sign a lease with her. 

What is the best way to deal with this situation? 

Should I just add the new tenant to the new lease through an addendum? I don't necessarily want to end the original lease and deal with the deposit since the tenant will still have all their stuff in there and I won't be able to see any major problems if there is a strategically placed piece of furniture.