I think you are in good shape based on the cases cited.
But I suggest putting it in writing to him and his sister that he and his sister voluntarily abandoned and surrendered the unit, returned the keys, and you accepted the surrender and he's done.
Keep it simple. One sentence does it.
I would not bring up any past issues because it appears that you failed to provide proper notice of those issues when they occurred (read the statute) so your intention to evict is irrelevant and will only serve to muddy the waters.
I also suggest (as a precaution) that you check the Monroe County court or a law library to see if a decision was rendered in that case. You'll want to make sure that the cited cases (they are old) are used to support the judge's decision or see if any newer cases were cited.
Other than that, if you plan on continuing to be landlords, you need to carefully and thoroughly study the statutes and learn the proper termination notice requirements for any breaches that occur. You need to jump on tenants the minute they get out of line or you'll find yourself losing a great deal of money.
Oh, one more thing, study the security deposit law. Even under the circumstances you are obligated to properly follow the law with regard to security deposits even if you end up applying all the current month's rent and the deposit to damage done by the tenant. This could come back to bite you if you don't get it right.