My fiance's aunt and uncle (his mom's sister and brother-in-law) are very orthodox Jews and follow strict rules when it comes to keeping kosher and keeping Shabbat (which is from sundown Friday night to sundown Saturday night). My fiance and I found a wedding venue that we love and are able to have a Saturday night wedding there which we really wanted to be able to do. However, the aunt and uncle, and likely one of their sons, have said that if we were to have it on a Saturday night that they would not attend. Additionally, even if we did it on a Sunday, they are not happy that we aren't doing the entire wedding kosher, but I made sure that we would be able to provide them with kosher meals and they seem to be somewhat OK with that at the moment.
I'll preface this by also saying that my fiance's mom does not have a lot of family besides them and his parents are divorced. The uncle also has Parkinsons and is not well at all and they live out of state so there is even a question as to whether or not they will even be able to come no matter what day it is.
He is very stressed out now because we truly want to do a Saturday night and 99% of our guests would honestly prefer not having to go to work the next day. I don't want to seem like we're being selfish, but it seems crazy to change to a day we don't want just to accommodate 2 people who may or may not even be coming.