If you are paying for the wedding, it's your choice who attends.
My auntie had split with her husband but rather than admitting that to my Mum, she came out with every excuse under the sun not to attend our wedding.
Firstly she told us it "had to be at the start of August as her children would be at University in September (when we'd originally thought of getting married). Told her fine, so arranged it for August to suit her family.
Next, said all her family HAD to stay at my brothers 2 bedroomed flat (there was 5 of them!) for the duration of their stay.
Said they could all stay at our house while we were on honeymoon but couldn't accommodate them before that time and brother didn't have enough room for them all to fit in (he was going to purchase an extra bed as it was but that the flat was simply too small to fit all of them in without my brother having to move out).
Gave them different options including their son staying at my brothers and the 2 girls at ours with the aunt and uncle at my parents house.
Said NO CHANCE.
Now, these weren't little kids but 20 yr old adults so perfectly capable of being away from mummy and daddy for a couple of days before the wedding then they'd all be together for up to a month while we were on honeymoon (we were also going to buy an extra bed for them so they'd all fit into our house).
But, trying to help I looked into b&bs / caravan sites / hotels in the area with varying price lists so they could remain together but was told - NO, either your brother moves out of his flat and we stay there or we're not coming!
Two of my cousins were meant to be the bridesmaids but no way were we being blackmailed into that as brother said he wasn't moving out of his own flat (we told him what they had said but put him under no obligation to offer them anything)
Told them fine, if they didn't want to come that was their choice.
Auntie then bitched saying her daughter's didn't like the colours of the dresses as they were "hideous" (a light turquoise and not garish as had even sent samples of materials and asked them to pick which one they liked or pick a colour they would prefer). So to be told they hated the colour THEY had agreed on was laughable.
Then sent me a nasty email (supposedly from my cousin but writing style was all my auntie) saying they wanted nothing to do with our wedding as suggesting they stay in a caravan was "galling" and disrespectful and that I was being a selfish bitch for not helping them in any way.
Well, this selfish bitch decided, sod them. If that's how they feel then so be it.
I asked another relative to be my bridesmaid.
On my parents request we sent them invites but never heard anything back and they didn't come.
Several years later other relative said they been telling everyone that "we didn't get invited" My Mum told them ALL the other invites (including California) managed to make it safely and was their choice not to attend but her sister still tried to blame everything on us being "unreasonable".
Do not bow to pressure. Tell them either they shut up and accept YOUR decision or not attend. That while you'd like them to be there, you will NOT be blackmailed into inviting people you neither know nor want at your wedding. If they don't like it, tough!!
They might boycott the wedding (like my aunt and cousins did) but that was their loss not mine. I had a fabulous time without them and their drama.
Aunt finally admitted she didn't want my mum to know she'd separated from her husband that year and would have struggled financially for the family to attend.
Had she been straight up with us at the start we'd have tried to help them how we could but she was looking for an excuse and wanted someone else to blame so she could tell her friends and neighbours etc that it was us that had been so nasty to her!! (the poor little me, so hard done by attitude) 
Needless to say, I don't talk to her anymore (save a Christmas card) and want nothing to do with her spineless kids either as not one of them attempted to contact us to find out what was happening and why suddenly they weren't going to our wedding. Simply can't be bothered with that - Life is too short and all that.
It's YOUR wedding so you decide who is and isn't going. My brother was an usher on the doors at ours and turned the parents of a friend (who had been invited) away as they didn't have an invite! They stormed off but the venue could only hold a limited number and had "presumed" they'd get in for the ceremony even though it was a private venue!! 
Same mum at her own daughters wedding then made a snide remark about wanting it to be extra special and not "hoytie toytie" like other weddings her daughter had attended (get the dig in there Mrs). Just smiled sweetly and said every wedding is special as its the BRIDE AND GROOM that matter the most and NO ONE ELSE!! 