Did he say that in front of the girls, Corbyns?
I have read over all the OP's posts to check, and I do not think that was the case.
Busybecca
The following day when he was up and about, the day started with them both screaming at him from bed to carry them to the toilet. Then they were arguing with one another over who he was going to dress first. They both refused to walk downstairs, wash their own hands, put thrir shoes on and demanded he spoon feed them their cereal. When we left they both whinged that their legs were too tired so he tried alternating pushing them both on their bikes but whichever one he wasn't pushing was screaming and stopping and crying. I didn't say or infer 'I told you so' but he was just excusing their behaviour and saying they were just tired
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I do reprimand them for being rude to DH but the fact that he doesn't means they continue to do it to him but not me or anybody else.
You have been very effective in everything else you have tried to teach the girls, so I suggest you have not really tried to reprimand them for rudeness, whinging, screaming, etc at your husband.
In the above incident you do not mention any reprimand at all but the unpleasantness clearly went on for a long period of time.
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I can't do it for him or they'll have even less respect for him than they do now - if that's even possible.
Actually, the opposite is true.
Right now the girls know that you will not treat them the way daddy does and he will not treat them the way you do. They may well have picked up that you have hoiked your judgy pants when it comes to dad's ability to wrangle them out to school. It was clear to him that you had found him lacking or he would not have tried to offer excuses for their behaviour. Children soak up the atmosphere between parents.
They know they are living in a conflict zone. They are misbehaving for dad's benefit because he is softer than you are, the same way that children normally misbehave at home for both parents even when they behave perfectly in school. They are letting their hair down in spectacular fashion. Many parents are surprised that their Little Miss Hell On Wheels is Little Miss All Around Good Egg in school. In your girls' case the misbehaviour you are describing is extreme. You have to show them that there is no conflict by demonstrating kindness, affection and devotion to your DH for their benefit.
You also have to teach them that the way they are treating their dad is not on and will not be tolerated. You have to teach them to speak politely and to say thank you to him. (Again, it is fine for them to ask him to get a tissue or to help them off the trampoline as long as the request is polite, as long as they say please, and thank.)
So you think it's a healthy dynamic ...for the op to have to swoop in and do all the discipline even when it's not a situation she's involved in? [Corbyns]
She is involved up to her neck in this situation. It is as much her doing as it is her H's. Both parents here have chosen to follow diametric opposites of each other's approach to parenting, perhaps in reaction to each other. Both are motivated by anxiety about the effect the other is having on the girls. Neither one is 100% right. Both need to compromise. Both need to address their anxiety. It will take a true adult to stop the madness and begin teaching the girls how to treat others.
They are currently engaged in trench warfare where the OP has actually gone so far as to set up a situation where she ended up restraining herself from saying 'I told you so' to him, trying to prove to him that her way was 'the right way' and his way is 'the wrong way', and he for his part has gone so far as to call her 'cruel' because he believes her way is 'the wrong way' and his is 'the right way'.
Neither one of these parents comes away looking good in these anecdotes.
This situation can resolve itself in one of two ways -
(1) The standoff can continue and the damage to the girls can mount.
Or (2) one of the grown ups here can climb down off his/her high horse and try something different that is very much needed here, i.e. to adopt the role of leader and to stop trying to 'win'.
Nobody can win, but the ultimate losers if they continue to play this dangerous game of chicken will be the two little girls who have enormous emotional needs that are being ignored.