OMG. Never ever would I got away with that - EVER!! You need a serious stern blazing row with your whole family stipulating what is expected of them. And if not they obey. It will be world war 3.
My mother made it crystal clear that all birthdays, anniversaries, Christmas was never ever forgotten, no matter what. Even if I had exams, holidays, working 7 days a week & penniless.
I used to hand make presents for my mum and dad as well as bought gifts and I would be looking for things in the sales, and all year around.
Massive amounts of effort was put into making cards, and exactly the right bought card as I trawled around the shops. I spent hours on EBay looking for exactly the right gift to make my parents smile & be delighted.
I bought presents even when I was penniless, and even wrapped presents when I was working 3 jobs a week/100 hour working week.
I handmade birthday cakes, Christmas cakes, and put in VAST amounts of effort.
I was told to use Google reminders for birthdays, so nobody is forgotten.
Even if your kids have nothing, they can hand make a card even from rubbish in the recycling bin and 10 minutes of their time, colouring in.
You have allowed this fiasco to grow by not laying down the law.
Expect to be treated like dirt going forward. Just because you refuse to have screaming matches so your kids never ever forget their duties within the family.
good luck!