Is SD20 mentally delayed in some way? Is that why she only works part time and does not drive?

If so then DH needs to teach her that taking other peoples things is stealing and if they are not returned she will have to purchase new ones and return them.

If she's not mentally delayed then I guess I'm at a loss as to why your DH is allowing his grown daughter to be a leach and take things from the house.

Of course you are not. DH has to teach SD she can not take things to her mothers, actually he had to since she was a child. You can't allow this girl to take whatever she wants to her mothers, she has to have respect for you, your house and this things. I've been there and of course I would be so pissed. 

If it were me, I wouldn't even let her borrow those things if she asked.  In my experience, you will never see that stuff again.  We have a large collection of movies and games and I always had a strict no lending policy.  We are not a library.  My kids had a ton of friends and every one of them wanted to borrow stuff.  The one time a had an adult neighbor borrow a movie, I had to ask for it back weeks later.  His wife borrowed my blender and broke it.  The dumbass was using it to mix cookie dough.

There is a word for taking something that does not belong to you:  stealing

That makes your SD a: thief

So you live with a thief you can't trust, and none of your possessions are safe.  In your home, which should be your sanctuary.  

So no, you are not overreacting.

SD needs to work fulltime, or go to school fulltime and work parttime.  If she works fulltime, she should be paying a nominal amount of rent, which you can secretly stash for her until she launches.  

Personally, though, I could not live with a thief.  People need to feel safe and secure.  She has violated your trust.

I understand you being upset and I'm glad your DH will discuss it with her.

However, I think your anger over this reflects dissatisfaction with the whole SD scenario.  Have you and DH discussed a launch plan for her?  What does he think?

To February, your last post. This failure to launch adult skid is a problem. And your husband created this problem. There is much in the way of great advice here. I will give you my opinion. "neither a borrower nor a lender be". Pure gold! Do not lend FTL (Failure To Launch) anything.

And time to get things in order in YOUR home. Time to Queen Bee the heck out of YOUR home. Because she is too comfortable and will not seek changes herself you must get this ball rolling. Trust me, they dont get better without a LOT of push, so stop being a doormat (as indicated by your assertion that you are asking if you are being petty).

IN my situation, luckily SD21 Feral Forger doesnt live with us -  refuse. She has asked. She STILL at almost 22 has no drivers  license, no job and might be taking like 1 class. She is dirty, mean, rude and lies and steals. And lives with her toxic mother.

I often wonder if we could have "fixed" her. Im good at pushing, but she has figured out that screaming and crying and acting crazy generally gets her her way and I wont live like that. So Id rather spend my time on SD14 Munchkin and not her.

YOUR SD. You cannot fix her, shes already "set". the best you can do is get her moved out ASAP.

No. You are not overreacting. She is 20. If she wants games at BM's she can use her own money and buy some. DH needs to let her know that this is unaccceptable. Otherwise there may be other things that make their way to BM's. Personal products that BM does not have the money to buy. BM is entertaining and needs good dishes. The potential is unlimited.

If SD does not return with the items, her dad needs to take his daughter to the store and have her replace the items with her money. Monetary consequences tend to sink in.

I don't think you're overreacting.  Having your possessions not available and where they're supposed to be when you go to use them is frustrating, and having a kid take your possessions without asking feels like a violation.  Especially a kid who is already past her expiration (I mean launch) date, is not contributing and doesn't appear to be making much progress toward independence.

I think it's great that your husband is going to talk to her and let her know that taking things to her BM's house without asking is unacceptable.  However, I think things will only get worse unless he has the more difficult conversation with her - the one about her future outside of your home.  Is this girl going to school?  If not, why is she only working part time?  A normal 20 year old who is not in school should be working full time and supporting herself, or at least trying to get to that point.  It doesn't seem like she's doing that.  She needs a launch plan.  If life is too comfortable for her at your house, and no one is pushing for her to become independent, it's understandable that she would be fine with the status quo.  It sounds like she's living an easy life. Not every kid is motivated to be out on their own, so someone might need to light a fire under this one. Your husband needs to let her know that her becoming fully self supporting soon is an expectation, and a plan needs to be put in place.

You are absolutely not overreacting. I felt the same way every time OSD would just help herself to my things.

She would take my clothes without asking, my curling irons, she took the karaoke machine that was for everyone. 

I would be livid because she didn't ask and just felt like it was her right to take whatever she wanted. To me that's no different than the co worker that eats other people's lunches in the break room.

I had to tell my own daughter, at about that same age, that my things were not HER things. Embarrassed the crap out of her, and she deserved it.

It might seem like a small thing ("It's just a cheap game, Daddeeeee. I was going to bring it baaaaaack.") But the real issue is that she felt entitled to take something that wasns't hers, without asking. She broke your trust and that IS a big deal.

my children knew that you do not use or take something that doesn't belong to you, unless you ask and receive permission. She's too old for this sh!+. Does she pay rent, buy her own food, pay a phone bill, etc? if not, maybe it's time to turn up pressure. she needs to grow up.

She is only working now because we told her after she graduated and turned 18 that she had to either work or go to school. So she is working part time.. enough that she could say she was complying with that rule.

Seriously, though, I think we all know that that means working full time, like an adult, not just whenever she feels like it.

If one is not in school at 20, one needs to start adulting. Part time work is for people who are in school. Or retired. Or wealthy and just working for something to do. If none of these apply, she needs to work full time.

Her taking your things out of your house? Oh, hell no.

Now, if she wants to take herself to BM's, for good, that would be okay. But YOUR things stay in YOUR home.

Nope, not petty at all. My kids have tried to take games to their dad's house because they aren't a "game family" and we are. Nope, don't touch my games. I have however gifted their family with some games at holiday times and such so that my kids have games there.