I'm seeing red and just need an in-law vent to clear my mind, so please bear with me!

My little sister is getting married in a few months. It's a child free wedding but my older daughter is a flower girl. When they made the decision to have no children we asked my in laws if they could watch our girls after the ceremony. They agreed and to make it easier on everyone since the wedding is about an hour away from in laws house I asked them to come to the ceremony so that they could watch the baby and be close to take the toddler after photos. DH and I are both in the wedding. Apparently at lunch the other day FIL told DH that he hoped we weren't counting on them to watch the girls for the wedding. We clearly were relying on them since they agreed months ago when the date was set. DH called MIL and ultimately there was no reason given for them cancelling plans to watch the girls but during the course of the call, MIL mentioned that they never got a save the date for the wedding and they saw ours on our cork board so they knew that they already went out. What?! Why would they need a save the date to babysit our children for my sisters wedding? This just seems beyond childish to me and I can't believe that now we have to find an overnight sitter for our two kids. Ugh. Am I nuts? Should I have had my sister send a save the date to my in laws who were coming to the ceremony at our request specifically to watch our children since literally every single other family member is involved in the wedding?

Anyone else have any in law drama and want to commiserate? I usually love my in laws but I just can't with this today.