Complicated here.
We only have dss, I don't have children. Dp and I earn a similar amount, though he probably has less disposable income as he pays maintenance and the mortgage (I bought my half of the house outright so don't pay it).
I take breaks from work though, so over the year our earnings and disposable income probably even out.
We have a joint account for bills, holidays, household maints, groceries. NOT gifts.
In theory he buys all the gifts for his family (which is bigger than mine - he has six adults and three children to buy for) and I buy for mine (two adults, two adult offspring). Same re friends if we buy for them.
In reality he leaves it too late, doesn't know what to buy, I end up doing it and his sisters comment on how much better their presents are since he met me. And I don't always remember to get the money back from him.
And some things get thrown in with the grocery shopping so get paid for joint.
Dss - used to be that we bought separate. But once we lived together we decided they would all be from both of us and we buy sort of half each - though what happens really is that I buy all the small presents, stocking fillers, sweets etc, and dp buys One Big Thing (last year a Kindle Fire). So we do a sort of reckoning after Christmas. Last year he owed me money and we agreed he'd give me £100 which was for all the presents I bought.
Last year I wasn't working at Christmas really - I had stopped to do my final law exam in Sept, then did some consultancy in Oct/Nov and by Dec was looking for a new assignment (which I started on 20th Jan) - so I felt slightly concerned that I was spending so much.
This year I will be working, albeit I have 13 non-working days in Dec so will be pretty low on pay, but am in work until end March anyway so no need to be concerned. So even if I do spend more, I'll probably not ask him to pay me back.
Plus we're going away to Scotland for Christmas with my family - we have to pay c£500 towards the house, so we're reducing gifts to make up for that, and we won't be able to pack too much into the car.