I love the idea of 2 moms doing the co-op as a group too, if/when it's possible. I could definitely use the socializing, and the kids could too. Usually DH is the one doing childcare on weekdays, but on weeknights/weekends it would probably be him & I together.
I will try to wrap my brain around how to set up a co-op, and you guys too... then we can try it out soon and modify whatever we need to. So far I was thinking we'll all need to know each other's usual schedules (knowing there will be exceptions), and some credit system for hours.
We'll also need to know what we each will do/not do for our own kids. Like for A, I always let her decide when she goes potty (we don't ever require it unless we're about to leave the house). Maybe a list of "we always..." and "we never..." type of rules for each kid.
The co-op I read about on MDC had each family start out with 10 hours or something, and then their hours were increased/decreased with each time they used the co-op or watched someone's kids. The accounts were kept in a notebook but email would work just as well. There was one person each month (or every quarter?) who was coordinator, who monitored and arranged the childcare requests & availability, so the coordinator job was had by everyone over time.
That's all I can remember at the moment... we'll figure out the details and get something going!