Troubles with couple on a lease

[Issac Lee]

Hi BP community! This is my first post and would appreciate your help in dealing with my current tenants. 

I rented a SFH to a couple that just got engaged. Rent is $2000+/month. At that time, I only screened the male partner b/c he was the one working in the relationship and his fiance was not. In retrospect, I should have screened both of them, regardless of whether they work or not. About 6 months into a 15 year lease, things get started. I get a call from the guy who is concerned about infidelity and that another man is living in the house. The guy spends large chunks of time away from the home for his job. I advise him that he is on the lease with his fiance. I gave him an out and said that if he wants off the lease, they both need to agree to leave. Then, once a new tenant moves in, they are released from their lease. He probably knew that she would not want to leave voluntarily, so, he hires a lawyer to evict her. She hires a lawyer to have an order of protection. So, her and her children are living at the home and the guy is in another state with his job. I consulted my lawyer and he advised to stay out of their personal issues unless rent is not being paid. So, of course, they both try to get me involved but I try to limit my interactions with them on these personal issues.

During their tenancy, the guy was the only one paying the rent. When the above occurred, he wanted to split the rent. However, I told them to work it out since I did not want to chase down rent from 2 different people. She never responded to these request. Later, he replied he would still pay rent until his legal issues with her resolved. He was current up until 2 months ago, rent stopped coming in. He is still trying to evict her but this is dragging out. He is more than capable of paying the rent but is intentionally withholding. Also, he kept insisting another man was living at the house and that she violated the lease. So, I sent someone to inspect the property and I can't find evidence of such. This seemed hard to prove unless I devoted a lot of resource and time. 

I think my next step will be to evict them. However, I am considering cash for keys with the fiance but not sure how willing she will be. She threatened to sue me for illegal eviction b/c I did not intervene in her fiance's attempt to evict her. She seems to know how to work the system and recently, I found out now that she was evicted in the past, which is why I should have performed a background check on both of them from the start. 

This is my first time going through the process of a possible eviction. Going through this has taken it's toll. At times, I just want to get it over with and evict them both. However, I hear that the evictions are time consuming and costly, so I wanted to see if there was any other way.  Any thought and recommendation would be much appreciated.