Who is being unreasonable?

[Deadringer]

I am staying with an elderly relative while their usual carer is on holiday. This has been planned for months and agreed by dh. Youngest dd is 11 and has some mild sn, it can be difficult getting her organised and out the door for school in the morning. Since I agreed to do this respite, dh has got a new job, its not stressful and they are very flexible, but being newish he wants to be in early, make a good impression etc. For the last few mornings (at my request) older dd (age 18) has been helping by getting dd11 up and keeping on top of her so dh can get her to school on time. She has also been supervising her homework etc. All good. However, Dh has recently started a class on a thursday morning before work, a leisure activity, not work related, and he doesn't like to miss it. However dd18 has a big event tomorrow night, she will basically be out all day and most of the night, probably until 4/5 am, and I suggested that perhaps she could lie in tomorrow in preparation for her long night. Dh is very annoyed that he will have to manage dd11 on his own and miss his class.
Aibu to say that dd18 has been very good to help out and that dh should step up tomorrow?

Whilst I agree about him learning to step up, as the OPs daughter has sn, it may not be as simple as just learning this for her. I work with adults with asd/autism/dyspraxia etc and whilst so many of them are incredibly intelligent, they struggle with organisation, social awareness and similar because of their issues. My DS9 has asd and he despises attention being on him especially if he is in trouble or has made someone angry or upset, yet for the life of him cannot just let certain things go, such as his bed being made in a certain way. Not to say I've never got frustrated or lost my patience when running late, but I can say with confidence it has absolutely no beneficial effect, and just makes the day more difficult for his teachers if he starts the day in this way, which obviously isn't fair on them or the other children in the class. In the absence of additional needs this would probably be a good way to deal with it but upsetting an 11 year old with sn then leaving them to spend a day at a new school, their routine disrupted because their mum is away and knowing their dad is angry at them just seems a bit harsh.

I have texted dd18 and told her to have a lie in. He is going to call dd11 then go to his class, and bring her to school when he gets back. I am quite sure that she will have forgotten to have breakfast and will still be in her pjs on his return but sure they will sort it out I suppose.
Just to clarify, dd18 is starting college soon and is completely free at the moment, I wouldn't have asked her to help out if she was at school or working herself. And dh has been doing all cooking, shopping, housework, etc while I have been away so he is not all bad. I suppose i have fallen into the role of default parent over the years, i am not perfect but i am definitely better at it. I am not excusing dh though, he is a shit dad in many ways. For dds sake I probably shouldn't have agreed to help my relative out, but dh was in a part time job when I offered, and I thought we could manage it around his hours.
Thanks for all the replies.

I would be most inclined to give DD18 a little extra pocket money (if possible) in thanks for the last few days, and to enjoy her event that little bit more. I'm sure she loves her sister and you all, and did it for this reason without question. But that little extra incentive might just show her how much you value her help with not only the SN but also the slight age gap involved.

In terms of your DH, his Thursday morning activity isn't work related and he needs to take one for the WHOLE team here and make a sacrifice this week, and put the others in the home team first. His eldest DD has stepped up well beyond her expectations as sibling this week, you his DW is assisting an elderly relative as we all hope others will help us when re reach similar stages in our futures.

I understand what PP have said re just getting your DD11 up whether she wants to or not and dealing with it, but this is easier said than done especially - especially with SN whether mild or not. If you're not a morning person you're just not

Well, he sounds like a peach.

Obviously it is her dad's responsibility to parent his child (which includes holding back from upsetting her before school of having age-inappropriate expectations of her capabilities), but both of you seem to think the nearest woman should have to pick up his responsibilities so he can have extra leisure time.

He presumably could arrange suitable childcare if he wants to go to a leisure activity, like other parents do.