Well, what a situation! Girl, you are ~~~and I will say this with kindness~~NOT superwomen. Husband's wake up!!!! This is something I know allot about. You did answer all your concerns and questions quite nicely actually.
Yes, consistency is the key word here. Adults like consistency as well. If the parents are off schedule, so are the children. Putting them in daycare from 9 - 5 is the best solution. 90% of daycare centers are fine. Rotating schedules are a nightmare!!!!!! Been there and done that.
Children are flexible to a point. Consistency helps with controlling behaviors because children are inherently routinal (sp). If you can change your schedule to reflect that, the sooner the better. One key componet, don't use your husband's schedule to determine you/the children and the routine's at home.
In-laws, your own family members and friends used as part of this componet, OMG you are asking for trouble 101. Especially in-laws, they don't appreciate the value of what {you} are doing with the children. I would eliminate them asap.
I think you have a grasp on the situation~~go part time and do what's right for your family. Good Luck!!