Here is the other question that sprang to my mind when reading this......do you want these particular rellies at YOUR wedding?
It's your wedding you should have the people you want there not people other people want.
Justly opinion sorry if I offend anyone
Just in response to this - and obviously its up to the OP with respect to the particular guests...
Both our parents contributed to the costs of our wedding - mine substantially more than DH's, but it was still a contribution. When we did our guest list, we included the family friends we thought our parents would like to invite. We showed them our lists and asked if there was anyone we had missed.
DH's parents - "You don't have to invite these people just because they're our friends". Well, no, but we want them there.
My parents (well, Mum) - "here's the people you've missed".
Now, most of those extra people I didn't know very well. But I had enough space at the venue that by inviting them, I wasn't excluding people who I actually wanted there. And so for me to have a few extra faces there which were important to my mother, while missing noone important to me, was a no-brainer. Especially when they gave us so much towards the wedding.
Something else to consider. But I would have only fussed if I was constructed by numbers and couldn't accomodate those people without removing my own friends - and I thin my Mum would have understood if that was the case.