Phoah, your story sounds almost unbelievable, too crazy to be true. 

Firstly, I'd change all the locks, and if your husband cannot be trusted with not giving your SDs spare keys, then I wouldn't be letting him have keys either, and he can just come home when you're home. It sounds abusive and controlling, but you do deserve to feel safe and at peace at your own house and it is unfair if your husband makes you feel that way. If he doesn't agree to that, then I would find temporary accommodation and pack all your important, sentimental belongings and beings (pets, kids?). I wouldn't trust your SDs either if I were you. I wouldn't be letting them back into the house under any given circumstances. If your DH wants to catch up, he can go outside of the house and meet them elsewhere. 

Secondly, are you in speaking terms with either of the SDs? If yes, then I would definitely confront them and ask them why they took things that are NOT theirs? You could probably even report this to the police, since it would be considered breaking in and stealing if they take things that are not theirs, so tell your husband that you'd be going to the police if he doesn't have the balls to confront them. Also, report them and charge them for trespassing. They shouldn't be letting themselves in and out of your house without your or DH's permission. They're not living there with you and DH, are they? Did you have any aggressive confrontation at the time she took all that? If yes, I'd file for an intervention order. 

And thirdly, you do need to seriously consider if breaking up is the best thing for you, because your DH sounds like he has a massive unaddressed divorce guilt, which is why he fears his grown daughters. Time to put your foot down, what they did is definitely crossing the line. 

I find it bizarre that your SDs have keys to your home, and can come and steal things and damage property while you aren't there. Neither my adult bios (aged 40 and 42) nor my SDs (aged 27 and 29) have ever had keys to our house.   Have you had any sort of relationship wtih them aside from the occasional looting raids?  If your DH cannot set boundaries with them, you must.  Have the locks changed and ensure they do NOT get keys!  Block them and the exW on your phone and email.  Set up security cameras to monitor who comes to the door.  Your story did ring some bells with me, in that the BM of my SDs used to try and get things from our home - she once reached past DH on the doorstep and snatched a picture off the wall!  But never anything like you describe. 

Maybe DH should get your stuff back so you don't call the police and file theft and vandalism charges against his daughter. 

I would absolutely involve law enforcement with this. 

Your husband keeps causing you problems.

This cannot be the first instance of them overstepping and disrespecting your home, your belongings and you.  Your husband continued to allow them access to your home and now that they have stolen actual things.. refuses to deal with them about it.  

He didn't even have to be particularly hostile to them either..

He could have simply said.  "Hey, you may not realize it but there were things you took that did not belong to your mother and some pictures that taken that were not your family pictures... can I come and go through it and show you what things may have been your moms?" 

Of course, now that all of that stuff is in their hands.. and if accused and if the history isn't good.. I would assume they will destroy what they have.. I'm sorry for that.

I agree about getting law enforcement involved. It's the only way to make this all end. These adults should never be allowed back into the house after stealing all those things, taking a knife to your table and stealing the photo of you and your sister. Your husband should want you to be safe in your home.

This has been your house for 16 years. They have no right to have access to this place if they are terrorizing it. If your husband does see this as an issue and continues to allow this that is a huge problem. I would rekey the home. If they ever entered again and took anything I would certainly press charges and send a cease and desist letter, if not restraining order. 

I'd make a simple statement to my husband. "I am giving you and your daughters 2 weeks to return my items or I will be addressing it with the police dept. I am changing the locks and making it clear right now that if your daughters enter my home it will be reported as breaking and entering and any vandalism and/or thievery will be reported and charges pressed. If you cannot abide by this, you may pack your few belongings and go live with your ex and your children. Their poor behavior stops right now and will not be tolerated again. "

then do it. 

Sue her in court for your stuff back.  You can not let her get away with this. Show strength 

Why is irrelevant. Don't waste your time on figuring out why they are the shit that they are, Focus on what they are doing.  What matters is that they are doing it. Focus on that. Call the police, press charges, get an RO/PO keeping all of them away from you and your home. 

Make sure DH knows that though he has no balls, you do and you will end them if they ever show their faces again anywhere near you.  Make sure they deal with LEOs any time they pull any crap.

Do not give them second chances. End them now.

Depending on your age, all of this- MAY- fall under elder abuse in addition to theft. 

I'd file a protection order on top of all charges the police may seek action on. There is no telling what may happen next.  

Please keep us posted. Stay safe.