It’s breaking the order and not a great start, but bear in mind flexibility will probably be needed your end too.
Dod you not get s caveat tfat states you can leave the country with the children for a maximums 28 consecutive days? That’s usual.
the weekend in advance, I’d suggest you state now that he either misses that weekend contact or gets two weekends in s row. But whatever precedent you set now will be expected moving forward. And could he manipulated for his benefit.