@Youseethethingis1 but it's not "at" the child. It's here on this forum. He's a baby he doesn't know it's his birthday. It's for Her! And that's fine - but admit it & then you see why he's angry. Op wants a party for her & his & her family without an integral part of his family. That's just silly. So yes treating new baby like crown Prince is ridiculous. He doesn't even know it's his birthday.
Next year or after he will. & then foot can be put down.
Feet can only be put down so often.
There are enough first wives club on here who would expect second wives & kids to move out of bedrooms & sit in the back of cars & basically not even order a takeaway if the dsc are not present.
I'm a step mum to adult step kids & grand kids & it's hard. So so hard.
Bloody hard on here for step mums and on almost every single occasion made worse by a dh being Disney dad ineffective arse on most occasions & not supporting 2nd wife.
There's situations on here where stepmum is expected to move out of her bedroom, her kids share while bedrooms lie empty most of a week for dsc to arrive every other weekend & even one case where a stepmum was expected to sit in the back of a car while dsd princess sat up front.
But new step mums putting foot down for no reason are making a rod for their own back .
It's a small child who doesn't know it's their birthday. It CAN be helped & the OP will save herself a TONNE of grief by fighting only the fights that matter. Delaying the (not such a big deal anyway in her words) party for a week will go a long long way with dsc & her dh.
If op starts digging feet in now, it will be hell.