Thanksgiving + Golden Child + Gaslighting

My in-laws originally agreed to come to our place for Thanksgiving like they have been for these past fear years. However, my fiancé's brother (the golden child), who knew we had plans (because we told him weeks ago) has recently decided that he wants his parents to come to his house instead. So, he asked his parents, behind my fiancé's back, to come to his place for Thanksgiving for the first time ever.

For context, he refuses to visit his parents under the excuse that he hates to travel (he and his fiancé travel internationally all the time). Instead, he requests that we all drive several hours to him, for birthdays, mother/father's days, and fall activities, etc. He only ever visits his family on Christmas Eve, or if there's a concert he and his fiancé want to go to. So, as you can imagine, my fiancé feels a little undermined.

What we've learned is that my in-laws love my fiancé, until her brother is in the room. She's hurt because, instead of just admitting that they prefer her brother's company over hers, my fiancé's mother spent 30min on the phone trying to gaslight and guilt my fiancé into letting them back out on Thanksgiving with us under the assurance that my fiancé won't be mad at them, or her brother, if they go. My fiancé stated that it's their decision, and refused to give them an out. Now her mother is upset because she "doesn't know what to do."

Was my fiancé right to be upset with her parents and brother, and to stand her ground about her parents making the decision instead of trying to get her to do it for them?