@MWT I beg to differ. It is a family day. We paid half of DS's wedding. 120 guests. Under no circumstances were: both grandmas, dd and bf, sil 1 and partner (the DC didn't fly from Aus), sil2 and partner, DH's Best Man and wife, my MoH and husband, three sets of God Parents (Our closest family and friends all of whom were involved in the DC's lives) not being invited. Same numbers on the other side, with close family members travelling across the world. I find it incredulous that there are young people out there who are happy to take thousands of pounds from each side of the family (or even one side) and then demand that auntie Mary may not be invited.
Both families met, the DC wanted a central London wedding which we could facilitate because that suited all guests the best. The DC had a guest list of about 80. Between us we and the Bride's family decided we would pay for: venue, reception (sit down meal), drinks (we picked-up that tab), bride's family paid for: flowers, frocks, photographer, invitations, cake, etc.
If the DC wanted anything beyond that, they could have had it but would have had to pay for it themselves. They didn't go down that route - dil (sensible girl) bought a frock for £800, found a 2nd hand veil. She looked absolutely stunning. They spent their own money on a fab honeymoon, partly to meet dil's family who didn't make it over.
A wedding starts with a marriage, a party is built around the marriage which is a celebration. When we got married, albeit decades ago, we discussed parents' numbers on both sides, including family friends who loved us and we them. Our numbers and size of tent were based around that. MIL sent my mother the list from their side of the family for the invitations to be sent.
In our world, that's the normal way of doing things.