There can be a lot of reasons why you stand firm in the schedule.
What I'm not clear about is, this appears to revolve around D18 getting to her event on time.
If this was just your H picking up D18 and taking her to the event, but the other kids were staying home with you... would you tell your H "no" and have your D18 be late to her event?
If it was someone else taking D18 to the event, would you tell them "no" you can't take her two hours earlier than the time I want her to leave?
From where I sit, the focus should first be on the kids. I think it would be OK for you to say "yes, under these circumstances, that makes sense and will work for me."
Just stating that you do not want this to set some precedence.
There's pros and cons to this and sometimes maybe too much wiggle room... still... it's something that I've stood by... it's about the kids...
