Old Tenant in Jail, I got leased signed by GF. Now he's back...

[Alison P.]

Hello, I'm new to all of this and in April purchased a mobile home park that was full.  I grandfathered in all the tenants and they all signed my lease except for one odd exception.  The original tenant of one unit was in jail for 2nd degree assault when I closed on the park, but his girlfriend was living in the unit (he had been there since 2015 before being put in jail for 8 months).  I did all the paperwork with her and she signed the lease.  His name is on the lease but obviously he couldn't sign it and still hasn't.  The 1st 2 months I owned it, everything was great.  His girlfriend even paid me early both months. Then he got out of jail... In the last 2 months the rent has been late and at the weekend we had a big issue with him and his neighbor over parking.  We tried to solve the issue but he was pretty aggressive throughout, especially when I asked him about paying the rent.  They still haven't paid the rent for July even though I have sent a reminder and a late fee notice. He said he would pay on Monday but didn't and now they are not returning my texts.  I'm wondering if, because he didn't sign the lease, and it's on a month to month (because she mentioned they may be moving and didn't want to lock into a year contract), that I could just send them a notice to vacate.  Has anyone else had to deal with someone/something like this? I would appreciate any advice. Rentals are in Missouri.