AITA for only having parents and siblings at our simple marriage without ceremony?

My fiancée (30F) and I (31F) will be getting married early next year on our anniversary. We are also expecting our first child shortly after, according to friends the process to acknowledge a child is quite difficult for same sex couples when not married and this is why we marry earlier than planned.

We wanted to keep it as simple as possible and opted for a simple wedding at the municipal office, and want to give a celebration in about 1,5-2 years once we’ve had more time to plan and save money. This type of marriage allows 8 guests, so some people (sisters husbands, children and stepmom) won’t be able to attend the signing. Theres no ceremony and the official part takes 5-10 minutes, this was communicated. Obviously we would’ve liked everyone to be there, but we chose to do it this way. We plan to take family to lunch nearby and go for a walk, and invite our friends over for dinner to celebrate. These celebrations are more important to us than the 5 minutes of signing. I’ll be open about the fact that there could have been an option of a slightly bigger marriage (40 people) and would allow for a ceremony, however this would cost 800-1300 euros extra and we just wanted to keep it small and not break the bank yet.

The issue is, not everyone seems to feel this way. Me and my fiancée both asked our two siblings as witnesses before the date/location was locked, even though I’ve always had a rocky relationship with my sister Isabelle (34F).

Isabelle called me last week and asked why we were getting married on the chosen date, that we could just acknowledge our child without marriage and marry later. I told her that we’ve heard that it’s a bit more complicated in our case according to our same sex friends with children, and that it’s our marriage and we want to get married on our anniversary. She expressed that her oldest daughter, Olivia (6F), really wanted to attend as she really likes weddings. I honestly love Olivia, and I would love to have her there. I told Isabelle that on the day itself it would most likely be allowed to let one extra person join the signing so Olivia could probably join, and that we could also record the signing or even FaceTime at that moment. We left it at that and Isabelle didn’t seem too upset.

Isabelle called me again today and expressed that she thought we were only thinking of ourselves and not about the feelings of the others, she gave me these options: Just having the witnesses attend(no parents), get the bigger location so everyone can attend, or she and her family won’t be attending at all

I told Isabelle that I was sorry that they felt this way, but that I didn’t think she had a right to demand these things about our marriage. The call ended with Isabelle notifying me that she and her family will not be attending.

So, AITA for planning a wedding at which only our siblings and parents will be able to attend the 5-10 minutes signing while the rest will have to wait and join us afterwards to celebrate?