Last Minute Grooms-woman

My brothers wedding is right around the corner. A bit of backstory; my sister in law wanted to have a court and my brother did not. It was important to her to have her sisters a part of the wedding. My brother wasn’t available to help with the wedding planning as there was a big event he had coming up with work and his fiancé was planning a majority of it. Some months ago I asked her if she wanted the family/me m to wear a specific color for the wedding (I had a suspicion we would be told things at the last min and I wanted to avoid that) At this point there was no court and I wondered if her family would be wearing something specific and if she wanted my brothers side to match. She didn’t answer the family part but she did tell me a color, and I ordered a dress in that color.

Some time passed and I saw she asked her sisters to be bridesmaids. He was I guess annoyed at this and decided to make a decision on his own. He assigned a religious duty to my husband and I. This came out of the blue. My mother asked him who I would walking with and he looked confused. She was asking on behalf of me since we were a bit confused if I was a part of the court. He said no one and I said “Im not a part of the court.” He didn’t add anything and ended up changing the subject.

We saw on their wedding website he ended up having choosing to have groomsmen.
This hurt my mom and stung me a bit too. I recognize this isn’t my wedding and I already and the wedding of my dreams. My husband and I chose and notified our court a year in advance and we wanted our siblings to be a part of it. I realized that If I wore the dress I ordered earlier I would look desperate to be a part of the court. So I ordered a different dress.
Sometime later they hosted a party for the court and parents. While we do have a part in the wedding we aren’t a part of the wedding court. The invite was not extended to my husband or I. However an hour or two into the party by brother asked me why I wasn’t there. He assumed my mom was going to tell me and apologized for not inviting me. I told him we aren’t a part of the court and he responded with you are *doing religious duty* and further apologized for him not being clear.
Now this is where I feel it getting sticky. My parents, husband and I feel hurt. But I’m reminding us that it’s his wedding not ours. Recently- a little over a month before the wedding- he asked me to be a grooms woman. It’s a bit difficult to be happy about this since I was the last person to be asked and so close to the wedding. I did tell him I wish he had asked me earlier. I can’t remember if he responded to that. I asked him what he would like me to do and he said just be there.
The different color dress I ordered just came in. I told him that since I wasn’t originally part of the court I didn’t want to look desperate wearing the brides color scheme and I had ordered a different dress and was in the process of getting it fitted. He said that’s fine you might match.
My mom is against me wearing the first dress and insists I wear the new one as I had already spent some money on this and did not agree how my brother is handling this.
Im afraid of “stirring the pot.” Being left out, being told last min and trying to keep the peace is making me not look forward to the wedding which is now less than a month away.
Do I do what the bride and groom ask? (I also wore that dress to an event for the bride and groom) Do I wear the new dress?
Personally I don’t want to wear the first dress. At the same time I’m afraid of wearing the new dress. And my extended family is aware of the drama and side with my mom.
We have not expressed our feelings with my brother or his fiancé as he is not one to care about others feelings and we don’t want to upset the bride. I was and still am afraid of a potential argument making it about me and causing a rift. I also feel the time to speak up has passed.