So, when your stepdaughter tells her father to "die in a hole", what does he do? If he does nothing, then why would she change? What does he do when they use bad language? Again, if he does nothing, there is no impetus for them to change.
How long do their visits last? Is there any possibility you could take your kids and leave them all to it for that time? Really, if they behave poorly and your husband does nothing to stop it, then he deserves to have to deal with it on his own.
You need to sit your husband down and let him know how unhappy their poor behaviour is making you, especially "that for the past few days I have been second guess my decision to marry". Suggest he gets some help with learning effective discipline techniques if he agrees that something should be done. If he doesn't, them IMO he's not really your "best friend" because a best friend wouldn't put you through this carp.
I guess when your children question why their step siblings get away with poor behaviour when they aren't allowed to, you could explain it's because their steps aren't fortunate enough to have a parent who cares to teach them how to behave well so that when they grow up they can be well rounded adults.

Yes I was wondering why their father doesn't set some ground rules when they are his house ?

You can't control how the children behave when they are with their mother, but you can have rules when they are your house.

To enforce those rules you need your husband to be united in the ground rules.

Also remember teens can be a handful.

He does have rules for them, and he has become very strict. He feels like every time they are in his care he spends the majority of time lecturing them. He is lost I feel, but I am just very amazed on how they act, I have never came across children that act like that in my life and I, myself have 17 nieces and nephews and 6 siblings. I feel bad when my husband and I talk about the girls, because when it comes down to it I feel myself comparing them to my children and I shouldn't because that shows favoritism and he wouldn't dare do that to me or my children. Maybe if my children were the unruley ones and his were the more well behaved ones he would, but he can't really say anything bad about my children. Except for the occasional leaving the light on or acting like a superhero once in awhile. my 5 year old acts like spiderman and runs and jumps and some times make annoying sounds, but hey, he's a boy. My two oldest boys are outside all day playing basketball, that is their passion and they take basketball pretty serious for their ages. And my daughter is on my hip the majority of the time, she is very clingy and can be very fussy. So I guess that could work on his nerves, but I can't really stop a three from being winy. the wining has also gotten much worse since we moved intogether and the girls started staying with us on the weekends. My children are far from saints and i dont want it to make it appear that they are but they wouldn't dare to act the way the girls do. They act up at times like all children do but it is usually just little bickering between the two oldest. I am able to do things with them without being embarrassed of their behavior, they have good manners and pick up after themselves. They are just total opposites. They even get stressed out when they know the girls are coming and they've decided they would rather stay somewhere else then deal with the girls, but I can't not allow that. I do not want my children to resent me because they can't stand their step siblings. It's just terrible. I'm completely lost and so is my husband. I feel bad for even thinking or second guessing him. But I feel that there is no hope as long as their mother is alienating their father. Seems like the things she says to the girls should be considered child abuse...atleast emotional or mental abuse...I do not known though. Just a thought. Danyele

But, is all your husband does, is lecture them? What consequences does he give them for their poor behaviour? As in, "when you speak to me like that, you have to spend time out/have your phone confiscated/not go to the movies/not get dessert/rake the lawn/weed a flowerbed/whatever" to give them the message that if they misbehave they will have to pay somehow by foregoing a pleasure or doing something unpleasant. Teens are great at switching off and not hearing the words.

If your husband is lecturing them all the time and nothing changes in their behavior then perhaps he needs to look at different lectures.

Consequences from actions - something along those lines. Rewards for good behavior, perhaps. At the very least civil behavior.

Your situation does sound very challenging and you have to remind yourself that it won't be so unruly forever. Children have a habit of growing up and moving on.

If your problem is so overwhelming that you both can't cope, then maybe some professional family therapy is called for.

At the very least it is good that you have a chance to let steam off here.

Welcome to the wonderful world of being a step-parent. My heart goes out to you because I have "been there and done that".

If you can get your husband to realize that he is actually doing them a huge favor by setting rules for how they are allowed to treat him, that will be the turning point. Parents who shrug off the (sometimes unpleasant) duty of teaching their kids how to behave in polite society are not doing their job, just as much as if they fed the kids bad food or neglected their medical needs.

I suggest family counseling for your husband and his kids, mandatory.

I also suggest family counseling first for your husband and his girls and later you, if necessary. It also sounds like he and may you needs a good parenting class. What he is doing is clearly not working. The parenting class for both of you could help.

Agree with the others, but I would suggest therapy for you and your husband, as well as parenting class. Until then, I suggest that you take your kids out for the whole day every time his girls come over. Don't even come home until it is their bed time. They need a break from all of this stress even more than you do.

Family counseling would help tremendously. You and your fiancé are in a very difficult place and are trying to toggle a very delicate situation. His children also need to know that there are boundaries at your house, what is and isn't acceptable, but they're also conflicted because of the mother, unfortunately. I have friends in a similar predicament.

Your kids, thank god they have their heads screwed on straight but I think you shouldn't worry about them so much because it sounds like they are pretty together know and how to behave appropriately. Kudos to you for being a wonderful mother, but you are obviously concerned.

I think family counseling, with ALL of you, would help tremendously. Perhaps a psychotherapist who specializes in family counseling with children.

Best wishes to you. FWIW, you sound like a great Mom and I think in the long term you'd be a great influence on these children (a stable home life) - something that they won't learn to appreciate until they are older. Not that the burden should be on your shoulder, it's not, just that you are also a role model. Don't give up on this guy. He sounds like a great Dad with a crazy ex. Nothing you can do about that. Just know it's going to be a long road, and lots of struggles, unfortunately.

agree with Popi, your husband needs to step up and take the lead in this situation. Rules need to be set and followed, with consequences if they are not. Unfortunately this can happen when two families combine. If you love him, you will accept his baggage and try to help him fix things. My stepchildren are in their late 20's and we have similar issues, so I can totally relate. Good luck

I inherited 3 step kids, ages 16, 14 and 10 - their issues were school truancy, drugs, drinking, stealing and unprotected sex. The 10 year old weighed 150 pounds and thought of herself as a baby, in every way.

Plus my ex would not lift a finger to discipline them. It was a tough fight every day, but they finally grew up more or less as productive citizens. I'm just sayin', it's very, very hard, but it can be done.