Tell them the truth, you want to rehab and sell, you want to move your mom in, whatever....
I believe in honesty but you don't have to be detailed about it.
"Due to some lease violations in the past year, we've decided not to renew your lease and expect you to vacate no later than November 15, 2018."
Yes, they may return the home damaged and dirty. But they would probably do worse if you left them there. Get them out, use the deposit, and find better tenants next time.
You can be vague and still honest . I don’t believe in lying and I also don’t believe you need to explain in detail your reasoning because as you pointed out it could mean damaged property for you . I would say something like this . “ I plan to change things up in the unit and I wish to not renew as a result of my business model I have in mind “
The change up is simply getting rid of them in exchange for better tenants . The business model is to not rent to idiots who break the lease in the future
I'd be afraid of retaliation if I were too honest with them, but I might go far enough to say "this isn't a good fit for either of us" and you believe in win/win relationships.
Or if you want to avoid being direct can just tell them you want to renovate the apartment, which is probably true to some degree.
But if they're asking you might just tell 'em...