I can understand why he's your ex.
Calling a grain man a simp, I've never even heard that word before.
But back to you. You are not a bad mum.
Do as much as you can, not superwoman amounts, when kids are at, would say dad's but that doesn't seem the right word, if you can batch cook for when they are there and have some time to do whatever home schooling you can.
Get everyone involved in chores, ours will vacuum because it one of the more "fun" jobs.
If they want boy jobs get them to do bins, recycling, heavy lifting.
But take a breather, have a family meal, play Uno or something and forget about what you all need to do for a bit. Put a film on they like, get some popcorn.
We are all pressure cookers waiting to blow, you wouldn't be human if you weren't.