Oh lavender, I am disgusted with your H on your behalf. How dare he be so inconsiderate! How much you got on with your mum is almost irrelevant - she is your MUM, you only get one, and once she's gone you don't have one around any more! (Sorry I know that sounds a bit bloody obvious but sometimes it helps to have it stated plainly).
Re. your nc siblings - I sympathise, being nc with my brother as well. It is a real shame that you have no one to go to the funeral with, unless the friend who HAS contacted you with support would be able to go with you?
I think it is perfectly reasonable to just go to the funeral service and then leave again, lots of people do. But there are all sorts of considerations - will you expect/be expected to travel in the family cars laid on by the funeral director? You can choose not to, just take a cab or get a hire car. Will you expect/be expected to speak at the funeral service? Do you know who the funeral director is, or indeed your mum's solicitor, because since you are nc with your sibs, you need to speak to someone who can give you the relevant information and the funeral director will (or should) know most of the answers, or be able to direct you to someone else who will.
Ignore your aunt. I had a well-meaning friend tell me that I should talk to my brother at my wedding, to which he amazingly came, but when I tried he just blanked me effectively so there really wasn't any point (but I suppose I could say I'd at least tried to be the bigger person and had it flung back in my face). Meh. That's just the sort of person he is.
When you say your brother is in charge of the Will, is he a solicitor? If not, even though he might be an executor, there should still be a solicitor involved (I know not always but there SHOULD be) so you probably will not need to worry about him doing all he should, as the sol. will make sure that it is done as it should be.
It does sound as though your H simply couldn't give a shit about your feelings as he's making no effort to understand them at all - perhaps making plans to leave him as well and start afresh would be a good plan. Do you know if you're likely to inherit anything from your DM, because it could be the escape fund you need.
And condolences on the loss of your mum - the serenity you're feeling is shock, I believe, so when it wears off expect some of the other stages of grief to kick in. ((((hugs)))) and
and
for you. xx