Mth-to-Mth Lease and 1 of 3 tenants wants out for my other APT

[Andrew R.]

So I have a 2-family rental property. 

Unit 1 - Rented Mth-to-Mth with 3 tenants on one lease 

Unit 2 - recently renovated 

The tenants in Unit 1 have been a bit of a nuisance with late rents and lately the rent has been coming in later and later. I only collect rent from a single person and don't accept separate rent payments. Rent is paid until al later rent is in. The neighbors have no problems with the tenants and they have been good to the people on the block. Mostly owner occupied townhouse properties. 

One tenant has a cat when the lease says it is no pets. 

One tenant who says he always has his rent available on time wants to put an application for the Unit 2 that was recently renovated and get a different room mate. He does not want to have a "dorm" or "bachelor" pad style place since his girlfriend often comes over. 

Based on NYS, can I have this person put an application in and if accepted with his one roommate (instead of 2) can I he then state to his roommates that he plans to move out? I assume yes since the lease is mth-to-mth. 

Does this then void their lease and they have to find another roommate or can I terminate their lease and give them 30-days notice? 

Just want to make sure I handle this appropriately.