I agree with you all but there more here then you all touching on.
My grandson mother put him up to a lot of things. She remarried how and still loves to cause trouble. If she can get my grandson to pull something on my son wife it has made her day. Be firm but loving. Invite them back but first instruct boyfriend that they owe you for the damage. Make them work to repay it. Yes, it can't be repaid but they need to know from him that there is a price for this behavior. Have him and them put the lock on the door out of money he would have given them for something. Have them also make a trip to the farbic store and buy you new material out of their money. Getting the message across that mom idea of funny will cost them darling.