@SKK01 - which came first - the plan for your dh to take the kids to Wembley, or you choosing the date for your party?
If your dh was already planning to take the kids to see the football on that date, and then you chose the same date for your party, then you are being very unreasonable to dig your heels in like this, and to pull your kids into it too.
But if you had already chosen that date for your party, and your dh knew this before he made the Wembley plan, then it is a bit unreasonable of him to insist on his plan taking priority.
From your OP it does sound as if the football plan came first, though, and you are choosing to make this a test of whether he can put you first.
I do empathise with the feeling that, as mum, your needs always come bottom of the pile - it is horrible to feel like that. But this is not the way to get your dh to appreciate how you are feeling, or to get him to want to change. If you force him to give up the Wembley trip, he will feel resentment and anger towards you, and in that frame of mind, he is not going to be able to empathise with how you are feeling.
So my advice to you would be to sit down with him and have a calm discussion. Start by saying that you will pick another date for the party - that will help get him on side - and then say that the reason you were digging your heels in was because you always feel,like you come last behind him, the kids, work etc - and that you need that to change. Then between you, hopefully you can start to work this out.