DH installed the chains on the doors tonight. They are good to go. I left a message with the landlord's wife explaining the situation. She disagrees with me and thinks they have rights but I informed her I will be calling the police if it continues and so will the neighbors. So she knows what's up. I will send them a letter notifying them in writing tomorrow. I'm hoping this will help.
Send the letter via certified mail.
And then start looking for another apartment. This isn't going to end well - up to and including when you try to get your security deposit back after installing potentially unlawful chains on the door.