AITA for not wanting my kids every weekend?

My ex husband and I share custody of our 10 year old daughter and 12 year old son. We have a 2-2-3 schedule which usually looks like I have the kids Friday after school and then he gets them Monday after school. I get them back Wednesday after school and then he gets them Friday after school and then the week flip flops. We've done this since our divorce 5 years ago and it works well. I'm a nurse in the OR so I schedule my shifts for the days during the week when they are with their dad and my one call weekend every 6 weeks is a weekend they are with their dad.

Recently, the kids said they want to try splitting up on the weekends, so instead of both of them being with one us during the weekend, one will go with dad and one will be with me. My son said he would make sure he was with me on call weekends because he can stay by himself if I have to get called in or can hang out at the hospital until I'm done. My ex is on board with this because he says it will allow us to spend one on one time with the kids and will allow the kids a break from each other (they squabble occasionally and annoy one another). While they have a point- sometimes it is hard to not feel like you are disappointing one by trying to accommodate the other, I do not want to give up my free weekends. It took me a few months to get used to not having my kids all the time after the divorce but now my weekends without them are filled with activities or travel. My ex agreed if there was a weekend trip I wanted to take he would be fine having both the kids that weekend but I honestly don't want to have to take his schedule into consideration when planning my trips, and sometimes they are spontaneous trips.

I was talking to my family about this at breakfast this morning and they are all kind of appalled by me not wanting to do this. My sister pointed out that if I was still married, then I wouldn't have all the child free time I have now and many mothers don't get a break from their kids like I do. My mom said she can't believe I'd deny my children quality time with their parents for selfish reasons like not wanting to give up my weekends. My SIL seemed to understand where I was coming from but said that she would still do it and just incorporate the child into whatever I was doing and pointed out my daughter would love to go on the NYC shopping trip I had planned for December and my son would happily join me for my Saturday morning spin classes. I considered that but my SIL loves taking her kids everywhere so I don't know that she is aware of how nice it is to just be an adult without the responsibility of a child wherever you go. They were really making me feel like an asshole though. AITA?