My fiance invited his brother on our vacation without running it by me first, advice?

My fiance and I are getting married in Reno next year and will be making the down payment and checking out the wedding venue in two weeks. We've had this vacation planned for the last 2 months as a time for us to relax, get away, party a little, and definitely plan our wedding with just the two of us alone. Well yesterday he tells me that he invited his 21 year old brother and his brother's friend to come along. I wasn't too thrilled at first, but I found out they are staying at a different hotel and driving themselves, so I was fine with it. Today I asked my fiance if he confirmed with his brother that he is driving separately, and he tells me that they will be driving with us and chipping in on gas money...but not to worry because "we are dropping them off at their hotel and they will have to find their own way around while we do our thing." Immediately, I got very upset because I knew this would take away from our time alone and we would be the ones picking them up all over the place in Reno. For the most part, I enjoy having alone time with my fiance on car rides and while we are on vacation. We do a lot of family functions (and I love his family like my own), he lives with his parents and brothers so I find it nice we get away sometimes. I was upset at the fact that he goes and invites his brother on our vacation without discussing it with me first. I mean if we had spoken beforehand then I would have definitely been a lot calmer and relaxed about it. He tells me that he swore he told me he asked his brother and his brother wasn't sure about going. I told him its the principle of it all and we should have talked about it first before he even asked him in the first place. Then my fiance goes on to say that we always do stuff alone and sometimes he finds it better if we have a group and not to be a "party pooper". This got me even more upset because I told him this was our vacation and we had no intentions of inviting anyone else and if so, we should have talked about it before. I said its somewhat romantic because we are planning the wedding, then he tries to flip it around and tell me "well you should have told me it was a romantic trip otherwise I would have planned something nice and made sure not to invite them." Long story short, his brother and friend are now driving themselves and we'll just meet up in Reno. Even though we are doing our wedding stuff, I know somehow those two will be tagging along wherever we go and I'm not exactly happy about that. Was I wrong for getting upset or does anyone have advice for the situation? I love his brother and all, but this wasn't exactly the perfect time for him to tag along (not to mention his brother will be going to Vegas in October anyways). A little help? Thanks!