School attendance

Hello all, I am wondering what sort of custody modifications I may be able to pursue because of my kids' chronic absenteeism that occurs on my ex's parenting time.

For reference, my ex and I currently have a 50/50 schedule (3-4-4-3) with our 10 and 9 year olds.

One of my ex's set days is Mondays. He is unable to get the kids to school on Mondays because of his early morning work schedule. I get the kids to school for him as a courtesy as I am available most Mondays in the morning.

But when I am not available on Mondays, even way in advance, the kids just....don't go. He doesn't ask to work a later shift. He doesn't ask my dad who lives 5 minutes away from him if he can take them to school. He doesn't have a backup sitter, nothing. The kids have missed 4 Mondays so far this year because he isn't making sure they can get to school.

In addition to this, he has not taken them to most of the school early closure or late start days that fall during his time because he "lives too far away to drive them back and forth for just a few hours."

I just got a letter sent home (kids use my address to determine school placement) stating that the kids have missed enough days to be considered chronically absent. I sent a copy of the letter to my ex, who told me that it's just as much my fault that this happened as it is his.

The only days that the kids have missed on my time have been "sick enough to go to urgent care" illnesses and scheduled doctor visits, which I try to schedule early or late enough in the day that they are still present for half the day. In all the years that we've done this (3 years), the only non health related time they have missed with me was 1 day two years ago to attend my mom's funeral. And the only Mondays I told him I can't do it have been communicated to him at least 4 weeks in advance.

I swear I am so frustrated that I just wanna rip my hair out.