Yes, it is not just your spouse.
My spouse and many other spouses on this site do the same thing.
I think it is unfair to the person to think they are perfect and not just simple human beings with faults like everyone else.
For example I don't think it is fair to saddle the next generation with the obligation to Save the World from its current woes.
They didn't start the fire...
But this is a strong biological instinct that is difficult for bio parents to control.
This is why many step parents including myself resort to disengaging.
We can't accept the bad behavior and keep our self respect and the bio parent refuses to see it.
So, we reduce or completely cut off contact, refusing to be party to a situation without a chance of improvement.
Your child is perfect? Great, you deal with their "perfection" all by yourself.
I am outski...

Do you have children not from your spouse?

Yep, my wife and I had our version of the situation you describe. We have had basically 3 arguments for our entire marriage. Housework, the SpermClan, and our son (my SS now adopted by me).

I wanted resolution and she would take the "What do you want me to do about it?" position. I really didnt care what was done as long as something was actually done and it was effective.

Eventually we worked out a compromise that worked for us. Basically I took the stand that if she did not like how I parented or dealt with the SPermClan she could step up and get it done before I had to but .... if she didnt then I would deal with it and she would have my back. I had hers when she took action. Our son is now 25 and has been in the USAF for 6 years. We dont have disagreements about the kid any longer. The SPermClan ceased to exist for us when they quit nearly all contact with our kid when he turned 18. He pretty much wrote them off as the toxic toothless morons that they are. Good riddance.

I solved the housework issue by outsourcing it except for basic clean up and keeping our stuff orderly. That we have figured out for our selves.

Give the tactic a try of giving her a choice of stepping up and dealing with her kid'd behavior before you have to or biting her tongue until the two of you can discuss it in privacy. Good luck.

I have the same issue with my DH over my 13 year old SD and he acts super defensive and says all I ever do is point out her flaws etc., which is not true. I think bio parents tend to overlook a lot when it comes to their kids, and they look at them through the "lens of love" whereas we as stepparents are looking at them through the lens of responsibility!!

I was about to start an almost identical thread like this today, when lo and behold... here this is.

Marriage counselor said, "In a marriage... 50% + 50% = ...what?" See answer below...

*Heavy sigh.* If you're really in the relationship together, as SHE is - so are you - and vice-versa... you're damned if you do... and damned if you don't (take some kind of action).

If you don't say something to the kids, you're doomed to have to deal with that behavior forever.
If you DO say something to the kids, SO will defend her kids like a mama bear and tell you that you need to run all those comments through her.
If you run all those comments through her, she'll take it personally that you're saying she's a bad parent.
If you disengage... she might accuse you of "checking out" or "avoiding" or "being passive-aggressive" or God knows what else. To be honest, disengagement is a good temporary tactic, but if it was going to be the final solution, I'd just as soon not be with her - I see it like we're ALL a package deal; them AND me.

I've taken to using "coaching" techniques, where I ask them open-ended questions that they have to answer. "You wanted to take a shower instead of doing some chores, which is fine, because the rest of us took care of the chores. But then, when we were all done with the chores, and you *still hadn't showered,* how did that work out for you? How did it work out for the rest of us? Do you think it's fair that we all did the chores with the understanding that you were showering, but then you didn't hold up your end of the bargain?" (I'll tell you how it worked out for him: As is pretty typical, SS14 didn't do any chores, he got to dawdle and play, DW put the football game on pause until he finished his shower LATE, and DW and SS got to sit and enjoy the game *without me* because I needed to go to bed on time to go to work the next day - IOW, SS14 was the only one in the house who got EVERYTHING he wanted).

Hold them accountable. Not just for them, but for yourself. Also, hold your wife accountable for the parenting. The answer to the above equation is 50% + 50% = FAILURE. Everyone in the relationship MUST do their FULL 100%. You're IN IT 100% or you're not in it at all. Best of luck!