Christmas plans, husbands sister is mad…

We were trying to make plans for christmas with my husband’s side of the family, my sister in law said she was wanting to start a new tradition since its her first year having a kid, she wanted all of her family & her husbands side of family to come over to her house and bring presents for her son and watch him open presents in fromt of the tree, the invitation was so uninviting to me, I have two very young boys who hardly get any attention at all from my husbands side of the family, and they are supposed to go to her house and watch a baby open presents all day while they get like 1 or 2?? We have only met her husbands side of family like one time so itd be even more awkward, Anyways we told her we already are very busy that day, which we are, we have had plans before she even told us about the nee tradition, and we told her she was welcome to come to our house on the day we have plans with the rest of her family and she got mad, she said she wanted to have soemthing at her house for once, and said she probably wont be able to make it to our thing, are we being rude?? I feel having her and her husband and baby, and my husband and our family with their siblings and girlfriend/ and boyfriend with their parents and our childrens grandparents would be a much better gathering and able to spend special time with each other being equal instead of us going where we dont know half people their trying to socialize & watch a baby who barely knows what’s actually happening open all his presents from everyone

what do you all think? are we being unreasonable?