I feel for you in having to deal with this. I have to respectfully disagree with anyone that is telling you to confront them and let them know it is NOT ok for them to do what they're doing.
NEVER confront someone you don't know, ESPECIALLY when they are breaking the law! You do NOT know what they are capable of and desperate times call for desperate measures--THEY are at a desperate time in their life if they are homeless & hungry. By calling the police, you are letting them know that it is not acceptable for them to be where they are.
The way I see it, they have already established themselves as criminals. The laws they have broken, just by your own account, are:
Trespassing
Breaking and Entering
Theft of property
Destruction of personal property
That's just to name a few. And I hate to bring up a worse side of this, but are you aware that a lot of homeless people carry weapons--maybe homemade ones, but weapons, nonetheless--for their own safety & security? (Seriously...if you were homeless, wouldn't you?)
The absolute last thing you want to do is confront someone in their situation...
I wish you safety & good luck in resolving this situation.