ExH and I have been split up for nearly a year. We’re leading separate lives in separate cities whilst trying to co-parent our 7yo and 3yo.
When we were together I did ALL the “life admin”, even in regard to his family - bought all presents, RSVPd to weddings and organised hotels, outfits etc, sorted us going to family parties, everything. I did it begrudgingly because I always loved (most of) his family and otherwise nothing would get done.
The kids came back from a week at his on Sunday, the same day as their cousin’s (exSIL’s son) 7th birthday. I commented on her Facebook post saying happy birthday Harry, but I didn’t check if the kids had spoken to him as, by then time they got home at 5.30pm, it had gone from my mind. May or may not be relevant - “Harry” is very spoilt and indulged, to a ridiculous degree, Ex and I used to refer to him between ourselves as Little Lord Fauntleroy. There would be an expectation from everyone to make a big deal about his birthday.
Yesterday I got a text from exSIL saying that Harry is very upset as he feels his cousins forgot his birthday - they didn’t get a call, a card or a present, and she “expected better of me” 
. She knows they came home in the evening and Harry was expecting a call when they got back. Now since Ex and I split up, I’ve maintained a good relationship with his family - mainly because I always got on with them, especially his mum and dad, and there really was no need for any animosity. But his siblings were always hard work and I wasn’t sorry to see the back of them. So I simply replied “speak to your brother” and thanked my lucky stars I didn’t have to please her any more.
Anyway today I got a text fro exMIL - who BTW I adore and she’s been amazingly supportive since the split. She said exSIL is obviously upset because Harry’s birthday was a bit naff in isolation and that was compounded by no contact from his favourite cousins - which she acknowledges is exH’s fault entirely. However she’s basically gone on to ask if I could carry on getting presents for their family members - on behalf on the DC and/or me rather than from ex - as she feels that otherwise there’s gonna be no presents at all and a lot of upset.
My first thought was “no fucking way”. Aside from the fact that I don’t want to continue to facilitate exH’s goal of being the biggest manchild in existence, I’m a single mum now and this could cost a fortune! His family is huge and even if I spent just £10 each on cousins, aunties, uncles and grandparents, for Xmas and birthdays that would be £400 a year!
However, she’s right about one thing - if I said no, there’d be no presents for them ever again. ExH has the unfortunate affliction of being lazy, selfish and tight fisted all at the same time. He’s not hapless or forgetful - but buying presents means taking more than 4 seconds to do something for someone else, whilst parting with his money, and he won’t do it. And he wouldn’t be ashamed about it either (you can see why he’s an Ex). His mum and dad especially deserve better than that. I’m not exaggerating when I say I’ll be amazed if DD gets anything from him for her birthday in a couple of weeks. So if I do say no, then my in laws will get nothing and my DC will be in the horrible position of being the only grandkids not to buy granny, grandad etc presents at Christmas - something they scarcely notice now but will do before long.
Good people of MN - what should I do?!