Tit for tat (step)parenting?

[Mueslimorning]

Dh is pretty rubbish at parenting his teenage dd, always was, probably always will be. Result? A willful girl with little or no consideration for others (I already had a short rant about her latest misdeeds on another thread...).
Our couple counselor has been adamant about his need to step up his parenting skills and I'm usually the one suggesting do-able compromises to restore balance. I've seen a lot of positive changes in my dsd 16 and work hard at creating harmony at home.
However, even when an amicable solution has been found, dh can't seem to let it go and then tries to make out my ds is a real pain....
I was momentarily stunned when dh yesterday announced that sometimes ds remarks make him want to slap him!
Dh has never lifted a finger against his own dc and I'm pretty certain there is no actual intention of following through, and yes, ds, 15, loves to exude a devil may care attitude, messy room etc, but mostly to hide fact that he's a real sweety, polite, considerate and thoughtful, def not a cool image at 15. And while dss has become more comfortable with our set up, dsd, when in doubt, becomes v rude and at times aggressive.
I feel dh cannot bear to have anyone see his dd as less than a perfect princess and it somehow reflects on him when she isn't.
I'm quite happy to discuss ds sins with dh and don't feel too proud to ask for parenting input.
I just can't get my head around the tit for tat, " my dsd was told off so now your ds will get a bollocking..."
May I just add that I leave the parenting of dsc to dh, dss has 50:50 arrangement, dsd visits eow, am supportive on the sidelines when he needs me. Dh is quite happy to actively "parent" ds, lives here ful time.

What a horrible thing to say to you about your ds.
My DP often seems to be delighted when my dc step out of line and get a telling off, I think this is because it takes the heat off his own kids and makes him feel less bad about his own parenting (or lack of it)
I totally understand the 'perfect princess' scenario. My DP is the same, DSD can do no wrong in his eyes and she can be very manipulative and sly to get his attention away from her brother.
DP saw her in action for himself this weekend (he heard her swearing and being vile to DSS from outside the room) and was shocked that his 'princess' could be so rude. I said maybe he had just seen his dd without the rose tinted specs for the first time!!! To be fair to him he did really tell her off because he was so shocked and I have to admit to being a little glad that he had seen through the act she puts on.

Thanks, Kaluki.
The weird thing in our house is that although both sets of dc have experienced parents divorcing, dsc problems (probably resulting from exw bitterness and control issues) would need more addressing but are played down, while ds has always appeared well adjusted and his "sins" are blown out of proportion.
This makes parenting rather difficult and thankfully we have a responsible couple counselor that insists on dh mending his ways... I just find him so predictably petty when he's overly critical of ds leaving used plates in his room for 24 hours, but dsd, who has form for,being a selfish bully, especially also to dss, is treated with kid gloves (it's like he's begging for forgiveness when even mildly scolding her for an unusually mean act).

Dh and ds have started a weekly activity together that should strengthen their bond, but ds has always been fond of dh from the start, so tbh I thought it would trigger some deeper emotions from dh. Instead he's been moaning that dss feels left out (they are v alike and share plenty of quality time and activities, it was living with us that broadened dss range of friends). Sometimes it even feels as if dh and dss really only want to bond with each other, regardless of other people around them... And dsd is their queen bee in charge!

That is exactly the dynamic between DP and DSS and DSD when we met. DSD was the mini wife and substitute mum to DSS. She ruled the roost and DSS and DP hung on her every word and were terrified of upsetting her!
Very strange imo