I don’t think this is about the party - one evening in two months’ time! - I think it’s yet another weekend when OP is left alone as DH is away looking after his mum. And OP has told us in another reply that she’d have to get dropped off at the train station if she wanted to go anywhere.
So I believe the reality is OP doesn’t drive and when DH is away she’s stuck at home, unless her friends come to her. She probably feels a bit of a burden to them asking to be picked up every time.
That’s how my own mum feels. The difference is, my mum is 80!! I’m 52 and OP sounds like my mum, not my peer!
OP I wonder if you’re over reliant on DH and feeling lonely in general as he’s away so much. Away both literally when he’s at his mum’s and emotionally as he’s working or sleeping when he is at home.
This party has become something to fixate on to avoid another lonely weekend.
The answer is not for your grown-up kids to entertain you. They need their own lives.
You’ve said you have friends, perhaps you need to rekindle some time with them. Just you and them. Don’t sit at home while DH works or sleeps or is away!
You’ve made a mistake about this party but I understand the reasons. The only thing I am going to criticise is this:
I don't think he's the one who doesn't want me around if you know what I mean
Come on now. That’s blaming DiL which is unfair.
Get yourself a life (I mean that much more kindly than it sounds!) and take more control of your time, fill it with things for you. Don’t sit around relying on DH or your adult children for the next 30 years!