My wife got into design consulting recently...and after I've been a 'freelancer' for the past 5 years, I had tips to share with her:
1) Despite common belief (and fear), YOU the expert are in charge. Not the client. You take the reins. You don't let them add things to the scope of work without expecting more money.
In your case, YOU are the boss. Not them. Fear of pushback or anything is not the way to go. Losing your cool with them on the phone puts you in a beta position.
2) Set expectations from day 1.
Unfortunately, sounds like you've already wasted a bunch of time on the phone with them.
I inherited a tenant a few months ago and they called me within the first 3 weeks at 4AM because toilet was leaking.
First, I didn't answer the call. Second, I didn't call them back.
Instead, I sent correspondence in writing to "train" them.
Also, I told them directly. "I promise to make necessary repairs within 48 hours (and I sent someone out that day). In return, I expect you to abide by how we manage our properties. First, don't ever call me, especially in the middle of the night. All requests go through email. Second, this toilet likely has been a problem for awhile (it was and rotted the floor beneath). It is your responsbility to tell me before problems get out of hand or you pay for it."
Haven't heard from them since except through email.
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Bottom line:
...you're the boss.
...you tell them how things go. Do it in writing. NEVER interact with tenants on the phone. I only talk to tenants on phone once and that's when I'm screening.
...if you don't have any legal way to get them out, someone recommended leaving X amount of envelopes with stamps and they can mail you a check.
Then, be clear with them that because they're being difficult, tell them now you likely won't be renewing their lease. You promise to answer repairs ASAP. In return, you expect them to follow your rules. If they are willing to get on board, tell them you'll reconsider.
Double-bottom line ---> you're the boss. Never let a tenant (or client) think they're the boss.