The short answer is no, you're under no obligation to change the consent orders.
Should you think about being a bit more flexible? Absolutely.
It seems a bit short-sighted to criticise the fact that the kids only spend two nights a fortnight with their step-siblings and therefore don't meet your expectations of having a close relationship with them, while simultaneously refusing more time for the kids to spend with their step-siblings to build a closer relationship with them. I feel like that benefit to the kids is the most obvious impact of trading weekends, surely mum doesn't need to actually say it for you to put two and two together?
I'm also not entirely clear on how they could possibly spend holidays with all the kids when the subject children and the step-children are on such different care schedules that they only spend two nights a fortnight together. Of course that's going to be hard - are they meant to just have two-day holidays each time, or should they just leave half the kids behind, or do you expect them to wrangle with both you and the other ex to sort out a holiday schedule that enables them to vacation with everyone?
This kind of inflexibility and lack of empathy is why ex-partners spend their whole lives fighting about the kids instead of just getting on with the gig of parenting. You need to ask yourself if you're refusing to shuffle care time for valid reasons, or if you're refusing just because you kind of enjoy the control and making mum's life difficult.
Word to the wise: If you take the high road and make concessions for her, maybe she will start making concessions for you, too.