your dad is a smart man! Do change the locks. Keep your home. Keep your kitties.
And frankly, I wouldn't allow AH to take more than his clothes etc....until he can pay you back the $1800. or..you can reduce the debt in exchange for items you wish to keep...others, you can accompny him to the pawnshop or list things for sale in the local paper.
If you should decide you will accept repayment..have it drawn up, but better yet...he should go get a loan for that amount, pay you in full and make payments to the bank.
This isn't cold and unkind.....this is how an adult man pays his bills.
and, ethically it was a theft.
all this is much easier and softer than if he were ever prosecuted for theft...hopefully with this kind of lesson of consequences he many be deterred in the future when he thinks about taking things that aren't his to take.