I am so sorry Kat, you are doing the work of 5 people right now and we all have a breaking point. You had yours and maybe there are things you could have done differently, but we all have reactions exactly in an emotional and exhausted state.
Have your spoken to D16 as to why she doesn't want to be there?
Perhaps this is the time now to set some boundaries on chores. Set a schedule for chores and let them know everyone needs ot work as a team because you cannot possibly work 70 hours a week and maintain a household and take care of everyone. It really is not possible without losing it at some point.
you have taken all the real responsibility since the divorce, now it's time to spread some maybe? One day they will look back and see it.
I give you much credit for all you do. A 40 hour work week, school, one child and a household to upkeep. I had to hire a cleaning service once a month I can barely afford.
I had to start early on with D9 and the chores because I simply could not keep it all up alone. She is responsible for her own laundry, straightening up, and unloading what she can from the dishwasher and clearing the table.
Please don't beat yourself up. You are an amazing mom holding it all together for your kids. One day, S21 ill realize all it takes into running a full household.