Hi OP - sorry to hear things are a bit distant with your husband, it’s not uncommon and as PP says it’s something you can work on.
I can see why you feel a bit hurt that DH is making a choice to spend that day with his mum rather than you and your DCs, but it can be like that unfortunately when family live in another country: it’s practical to spend a couple of weeks and understandable to want to see his mum
especially as she won’t be young. Just give him space/let him do his trip with an open heart.
Re doing something when he is back; I think 100 per cent he wants you to do something when he is back 😄
We are all children in a way, and like attention/bring spoiled/someone showing us we are important. I am hosting a 50th party today for a friend- birthday was 2 months ago but this is the first date that we can all get together (due to trips/people having Covid etc)… it’s not weird to plan something a bit later or have a few different events when it’s a milestone birthday
I get that maybe you feel like you can’t win due to your husband feeling pressured about money - I think nearly everyone is more worried about money now than we used to be. The party I’m having is at home, and I don’t think having a party needs to be expensive - you’d just plan the food and drink carefully.
I’ve done a couple of things to make today a bit special for my friend: a ‘happy 50th’ ballon, some bunting, and bought a special ‘happy 50th’ glass, and we’ll be having birthday cake of course - otherwise it’s just a normal having friends over, but it’s a nice way to mark the day. Maybe you could tell your husband that you will arrange something to mark the occasion when he is back, then think about what us best re timing and budget when he is away
Is it just his mum, or will he also be seeing his siblings & other relatives? That is another reason to stay for a while I guess