Crazy tenants – please advise!!?

This is my third post about this matter and I really appreciate everyones advise. As you may or may not know, we made the mistake of locking in a tenant into a 3 year lease that has been horrible from day one – that are aggressive, vicious, constantly causing trouble and are very clearly trying to get money out of us. We recently had a situation with the heating of the house that we fixed within 24 hours. Since then, we have sent them TWO certified letters in the mail, none of which they have signed for.
The most recent is an important letter stating that they are in breach of contract. Per the advise of people on this board, we sent them a letter after they REFUSED to confirm the names and number of people living in our house. We have the original names from when they first moved in on the lease but our township recently sent us a form that they wanted filled out w this info (and we are suspicious that someone else is living there anyway). They refused to give us this info and we sent them a letter stating they have a week to get back to us with the name and until then they are in breach of contract. The next step I am assuming would be to send them an eviction notice but at this point, knowing how vicious they are, I’m scared. Every time someone goes to the house, they scream and yell and intimidate them. If they aren’t accepting our letters, what can we do? Essentially they won’t let us communicate with them (despite the fact that they constantly send US letters).
What should we do? They are very much so after us and since they are pretty poor, I wouldn’t be surprised if they have played this game before to bring someone to court. What does one do when they don’t sign for letters? If we evict them, do they have to move out? How can they refuse to give us this basic information?
Please advise on what we should do next:( Thanks so much!