Here's a blow by blow update:
Tuesday night Summy finally started being successful on the potty. (5 total accidents) Jack stayed dry all day.
Wednesday Summy had 3 accidents, Jack 2. Pretty good day. Jack asked if we could "please wear underwear again tomorrow"
Today: Jack had 2 accidents, one being a "#2" (that is just awful I will say) and Summy's had 1 accident, but hasn't pooed in 3 days.
I am thoroughly exhausted and hopeful that with my husband off tomorrow afternoon and the weekend, it's going to get a little bit easier. So far it hasn't been too bad but doing it mostly alone has been exhausting.