Oooooh, there are 2 things guaranteed to cause a rift in a family. Funerals.......and WEDDINGS!
Me and my husband got married in the early 1990's, and we both had fairly poor and quite infirm parents with no money or savings. So we had to fund our wedding ourselves. We paid for everything; the ceremony, the reception and meals, (pub lunch,) the rings, the flowers, the bridal dress and suit, the photographer, the wedding rings, and the honeymoon (a weekend in the Cotswolds.). Won't go into how much each thing cost, but the whole lot cost less than £700.
We could only afford a very small wedding, and excluding parents and siblings, I had about 26 extended family members (cousins, aunts, uncles etc...) And DH had about 12-13.
So we decided to keep it down to DH's nan, (his grandfather has passed by then,) and my grandad, (my nan has passed by then,) my folks, his folks, both brothers and their girlfriends, 5 mutual friends and their partners, and his BFF and my BFF and their partners. Around 24 people in total. No-one else.
After that, around half of my extended family stopped talking to me, and I was regaled - EVERY TIME I went to my parents house, with a tale of how 'upset and devastated and hurt' my auntie Barbara was at being left out of the wedding, and how 'angry and furious' my cousin Lyn was. And my mother asked me at least once a month why I didn't invite 'my own family!' 
Despite being told many times, (by me and DH,) she seemed to totally ignore the fact that inviting them all would have ended up costing us more than double, with 60-70 odd people at the meal, and the bigger room at the register office.
I told my mother that my 3 female cousins close in age to me (who got married 2, 3, and 5 years before me,) had their weddings PAID for by their parents, like the whole kit and caboodle; the dress, the flowers, the reception, the photographer, the honeymoon - EVERYthing, and we had to do it ourselves, so they had no right to judge, and demand that they are all invited.
As i said, about half of my 2 dozen or so extended family members that weren't invited to my wedding stopped speaking to me and DH - although his 12 or so extended family who were not invited seemed to be OK with it, it was just mine who kicked off!
After all this, me and DH were not invited to ANYthing that my extended family had. Christenings, 40th birthday parties, weddings, Christmas parties, 21st birthday parties, you name it; everyone was invited except us. This was despite us inviting them to various parties and get-togethers afterwards. We had out first-born Christened, and invited all 25-26 of them (because of the shit we got for not inviting them to our wedding,) and only 5 or 6 came.
Even 10 years later, half of them still had a stick up their arse and were still ignoring me and DH, and our kids too. And even the rest of them rarely bothered with us as they sort of 'sided' with the rest.. We moved out of the area not long after (about 40 miles away,) some 10-12 years back, and have no contact with any of them now, except my brother and his wife and their 3 kids who moved away too and only live 20 miles from us. He sees them occasionally, but we never discuss them when we meet up 3 or 4 times a year. (Both sets of our parents, and our grandparents have all passed now by the way.........)
All this, from not inviting them to my wedding Pathetic eh?
I did hear though that the one half of my extended family don't speak to the other now though, after a big massive row over some borrowed money, and they have massive arguments on facebook at least once or twice a month!
LOL, I am better off out of it, and I don't need them anyway, as I have my husband and kids, and his family. (As well as the families of my adult childrens partners!)
I did used to be hurt at being 'pushed out' of the extended family, but this past 6-7 years I have not given a shit, as I realised they are all a bunch of mindless chavs who brought nothing to my life anyway.
But yeah @mumwhite PLEASE don't hold a grudge against your nephew; he and his bride to be, probably just need to keep the numbers down. My extended family made me feel like shit for YEARS for not inviting them to my wedding. Please don't do that to your nephew.