agree, i would do the same

they violate lease first by putting those inside garage without permissions. they need to be fined and notified - even if you might want to allow them doing so in the end but make sure they add some rent or penalty into your income. bottom line is: they spent so much time and effort into this unit they DO NOT want to move out. On your side make sure they know you CAN FIND another renter right away.  good luck.