I have two brothers, an older brother who is 2 years older who I am not close to (and FI can't really stand) and a younger brother 3 years younger who both FI and I are close with. So when we decided on our WP my mom was all upset my brothers weren't included because she thought that's what you had to do. But, I wasn't going to force my brothers onto FI (he would have been happy to have my younger brother but just doesn't get along with my older brother) and I had girls I wanted on my side. So I made them ushers. I thought this was perfectly acceptable and even talked to them first about it to make sure that they wouldn't be offended. They were fine with it which made mom fine with it.
So we have now picked out our tuxes and included my brothers on the list to get fitted. My younger brother may not actually make it to our wedding though because he plays college football and has a game the day of our wedding. I'm upset by this but have come to deal with it and know it is his decision and that he has a committment to his team. So it may just be my older brother as an official usher (GM will help seat people too though). And, if my younger bro can make it, the $150 for a tux will frankly be tough on him. Especially since he'll have to travel to the wedding. My older brother can afford to rent the tux but he's getting married this year too and also has to travel to the wedding so it's a lot for one day IMO. I have boutonierres for them. But, do you think it would be okay to have them just wear dark suits (black or charcoal) or is it really necessary for them to have tuxes? Our event is "cocktail" attire so most people will be in suits, not tuxes.