The fact is, there is room for everyone's in-laws. Middle sister is divorced and all the other in-laws are now invited if they want to travel from Michigan (for youngest sister) and Iowa (for brother). My in-laws are the only ones who live in town and I haven't actually talked to them yet about this -- I did tell all my siblings first before saying anything to my in-laws. As far as parents' brothers and sisters -- my mom isn't speaking to one of her sisters and we can't invite the others without inviting the one my mom isn't speaking to (another long story there!) and my dad is an only child. I ran it all by my mom first and she was fine with it and she is the guest of honor.
As far as the flowers and flutes go -- my mom was pregnant with me when my parents got married, so they just went down to the local courthouse and got married -- no big party or anything, they didn't even have a honeymoon. I thought the flowers and flutes would be a nice touch since they didn't have them at their wedding. I actually thought this was a compromise between the huge affair my youngest sister wanted to have and just dinner out with the folks which we do a couple of times a year anyway.
