Congratulations on the new baby and the promotion! Sounds like you've got a lot going on
You're definitely at the top of the market for two kids in NW (not that there aren't nannies who make more, I get), but you could find someone really good for $18/hour, plus OT, plus federal holidays and 3 weeks vacation. By insurance, do you mean health insurance? And by phone, as in you pay their cell phone bill? If so, you could definitely find someone great for $18/hour.
We have au pairs, but you really cannot have them work more than 45 hours a week. And they usually require a ton of time to choose, train, acclimate, and generally take care of during the year. Hard to find with lots of infant experience also, especially since you're talking long hours with a really young baby. If you did go the au pair route, I would suggest taking a long time to look and hopefully you could find an older, independent au pair with infant experience. If you talk up a set schedule (say nine hours each weekday with no weekends/evenings ever), the separate big living space, and free use of a car, you might be able to find a good fit. It might be great for you since your husband's schedule changes.
However, finding a part-time nanny to cover the other 10 hours or so (assuming you are working 50 hours plus commuting time) would be really difficult. If you could definitely keep it under 45, that would be a lot easier. Otherwise, I think you'd be stressing every week trying to find someone to cover a few hours here and there.
I don't know about live-ins, but it seems like the only reason you'd want a live-in is to save money as compared to a live-out. And you're right that there are some crazy high quotes on here whenever we discuss live-ins. I'm not sure what's normal for a live-in, but I agree personally that if all you find is live-ins around $700/week, then just go with a live-out and suck up the money unfortunately.