You guys have been married for 4 years, what's changed? Has she treated your daughters badly all along and you are just getting fed up with it?
I would never treat my SS this.  And my DH would not take it lying down if I did.

I think your wife owes you and your daughter an apology, and you need to talk to your wife, set standards for her behavior around your kids, and if you are unable to do that, then counciling or divorce.  I love my SD, but I don’t like her very much, and sometimes it’s hard for me to come up with nice things to say about her, but I would never put her down, maybe some constructive criticism in private, like “hey DH, SD sure seems to talk about her accomplishments a lot, it’s rubbing off on our younger kids, maybe you can ask her to tone it down, after all it’s hard to make friends when you only want to discuss you.”  He probably didn’t like that too much, but oh well.  I might give her a smart comeback she might not like if she wants to aim some disrespect towards me, but otherwise, if you can’t say something nice don’t say anything at all.

OP your duty is to protect your child that you wrote you know is right.  Your wrong, you are not required to "SUPPORT" your wife. she doesnt need holding up. That is what support means.

You want to support a woman who treats your daughter like junk AND her kids steal from your home too. That does not make sense to a reasonable person.....again, she treats your daughter like dirt, her kids steal. And you feel a moral obligation to "SUPPORT HER".

Do you want to live like this for the rest of your life?????

Your wrote below:---------------------------------

So, how am I supposed to handle this?  I know that my D was in the right, but I have to support my W.  To make it worse, my D has never taken anything from the SD's, but the older SD has taken SEVERAL things from my D, and we have found only SOME of them in her closet at my house and some at her closet at her dad's house, but it's my D that gets yelled at.

I’m going to play devils advocate here, on one hand if what you say is true, then your wife is being emotionally abusive (did she even want to go on a family camping trip, have the two of you had a holiday alone together recently. Kids don’t need holidays as much as we think they do). Secondly, be absolutely sure you aren’t being played by your daughter, or any form of communication could backfire, said in the wrong way at the wrong time. Just be sure, and be careful.

I am surprised that posters have been so kind to you. We all get that step mothers are wicked witches whose dearest wish is to shove their husbands' innocent children into an oven, but your post is oddly one-sided and totally sympathetic to your daughters at the expense of your wife. She is supposed to be your Number One and Love of Your life, not some lowly dogsbody to cook and clean and make a nice camp site and act as a punching bag for your offspring. Step daughters, which is what your girls are to your wife, are notoriously difficult for women to deal with, and to put it kindly, the troubles are not always solely becuase the older woman is jealous, crazy, etc No doubt there is trouble in paradise, but I would take a hard look at what is acdtually going on in the relationships among the women in your household. I can promise you that, at a minimum and regardless of the truth of the matter, your wife is feeling mobbed by your daughters. Try to understand why and you will be a long way toward figuring out how to salvage the situation, if that is even possible.

She (foolishly, I believe) did you a great kindness by attempting to take on you and your brood. Please give her credit at least for that.

Ummm... damn. I'm sorry this is happening...

I guess first thing, what's changed, do you expect your wife to have a lot of responsibilities with your daughter? Things like that can slowly build up resentment.  Are you prone to buy them extra things all the time? Spoil them? Do they have attitudes?  There's two sides to every story. I'm willing to be that she has a side too.

Obviously her behvaior is NOT OKAY at all. But I know at least when I act out, it normally has a root source, and sometimes it's subconcious and I have to sit there and think to figure out what's got me so frustrated. It can be anything form being stressed, to little things that have been said and built up over time. (I say act out because I'm aware of the thought and typically don't let the behavior cross over.  So I act MOSTLY fine, just interanally screaming, lol). 

I know that's not everyone, some people are honestly just a$$holes for no apparent reason. But maybe there's some kind of cause?  I feel like if there is, pinning it down and figuring out a resolution may be a better long term solution that eternally arguing, and your daughter DEFINITELY should be treated better here too!

I think talking to her is a good choice, ultimately, you need to protect your daughter, which means either figuring this out and coming up with a PRODUCTIVE solution, or getting her away from it.  Just keep in mind. Your wife probably isn't the only one causing problems.

"It's funny how judgemental some of you are without knowing anything."

Actually some of us here know quite a lot, having seen most of it all again and again and suspecting that your situation, in common with everyone else's, falls into the patterns and categories we've seen so often. If your situation is unique, though, please feel free to look for unique solutions. You probably won't find any on this forum from these posters, because we're working from well-known human behaviors that we ourselves have seen repeated again and again.

So take our advice or not. We are telling you to start by listening--really listening--to what your wife says. Imagine for a moment that her perspective may contain some truth, just as does that of your "girls." If you can't do at least that, this is probably the wrong forum for you.

I can't stand my SD but I would never show that to her or mistreat her. You need to have a serious talk with your wife about the way she treats your daughter and the reasons why, especially since she seems to be singling her out. You shouldn't have to stand for your kids being treated like shit by someone who is supposed to care for them, or at least treat the kids as if they do. She expects you to treat her kids as your own, but she won't extend you the same courtesy.

Sit down with your wife and tell her how you feel, that she is mistreating your girls. Being a step mom is very hard, complicated and challenging in many ways you can never imagine. I can tell you one thing, women start being mean towards their step kids for a reason, resentment builds because of a lot of reasons that you may not be aware of. It may not always be what the step kid did or did not, most times it's what the biological parent does and doesnt! For example i started resenting my step kid because his dad treated him like an egg and like a royal prince, he had to get away with bad behaviour, he had to get away with doing no chores and what he wanted mattered so damn much as if he is a royal prince! I hated that DH would make excuses for SS's bad behaviour always, it was just pathetic and disgusting to me, I hated that he had unrealistic expectations like me loving his son or seeing him as my son or our son *nea* when HE IS NOT!!!

I hated that he made demands and expected me to labour for his child as if it was my rightful responsibility, he expected me to do far more than i was willing to. I hated that he would play video games with SS until midnight and i would feel so invisible and neglected.

The list is endless but my advice is talk to her, there is a reason behind her resentment.

You do not have to support your wife if your wife is wrong. Particularly after her proven history of being a witch to your two youngest daughters.

All else remailing equal, you need to put your figurative foot up your DW's ass .. in private .. over this.

My comment is based on the assumption that you are not a Disney dad whose daughters have not put your wife through hell.

Only you know the interrelationship dramas that have led up to this current crisis.