Wondering if I can get some feedback on this

My fiance and I got engaged in November and set a date in January for our wedding to be in June on a Friday. Everything has been going really well, no set backs or anything until just recently. I found out a few weeks ago that my FI's uncle and a few other members of their family are wanting to have a family reunion next year, and they want to do it the same weekend as our wedding. While I can understand their side of the issue (it's convenient for them), I do not agree with their decision. I feel really bothered by it because they never asked us directly about our feelings on this decision. It also adds more people to the guest list, and the reunion is becoming the big priority instead of our wedding. Another issue is that the place they are planning to have this reunion is an hour away from where we're having the wedding, so we know that some people will be coming to eat our food and then cutting out very early. This wedding has been a long time coming (6 years) and it's very important to me, especially since my parents are paying for everything. It also means a lot to my parents to give this gift to us, and we set a budget and a number of guests that we can accomodate. My parents have already exceeded their original number by 50 to make sure that we would not have to cut family members from either side. For them to do this without any thought or consideration to us or my parents is frustrating, and I feel like it's disrespectful. My parents also feel disrespected and are not happy about this. I don't think there's any malicious intent or anything nasty like that. I just think it's a case of a few people being thoughtless. My FI is going to send them an email tonight to essentially let them know, in a firm but empathetic way, that we would really prefer for them to not have this reunion the same weekend. What do people think?