I'm Lucy, and I'd be happy to answer your questions today. I'm sorry to hear about your situation.
You do have a right to serve another notice to cease smoking in the premises or vacate, along with a notice to pay the rent if it's still late at the end of the grace period, AND a notice to remove the other person now living in the premises or vacate. All of those things are grounds for terminating the lease (unless he resolves the problem). You can subpoena the neighbors to testify as to what they're observing and why they believe there's someone else living in the property. It could be frustrating, because there aren't any guarantees that you'll win with something like that unless he admits that the person is living there. Smoking in the property is also tough, because it's really hard to prove a smell in court - there's no way to capture it and present it to the judge like with sound or problems you can see. Using drugs in the rental property is ALSO grounds for eviction. You have the ability to list all of those violations on the Notice to Quit and then file for eviction if ANY of them is not resolved by the date you give. If he's not picking up certified letters from you, you can have a friend knock on the door and hand him the notice. If he refuses to take it, the friend is allowed to place the letter on his feet and walk away - he's still considered to have been given it.
Since you've got a tenant who appears determined to abuse the system, it may help to have a local attorney draft the notice for you and file the eviction if necessary. That way, you have someone who knows the system on your side.
If you really just want him out, you could simply offer to pay him to break the lease (or agree to return his deposit). I know that's probably not something you want to do, but it could be easier than evicting him at the end of the lease. It might at least be worth considering how much a lawsuit would cost (especially if you have to hire a lawyer), how much money you'll be out if he overstays his lease without paying, and the time involved in evicting him to see if that's an option worth pursuing.
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