I haven't had my second yet but I've been thinking about this a lot so I'll share my plan.
First I'll call DH to let him know that he shouldn't get too involved in anything at work.
Then I'll call my good friend from the birth class we took during the last pregnancy. She has a son just a couple days younger than mine. She'll come over and they boys can play that way if it gets to be too much too quick, somebodies there.
When things are really rolling I'll swap out dear friend for my doula. I'll also call my MIL to let her know she should be ready for the call to come stay with DS.
DH will most likely come home around this point if he hasn't already gotten home.
Once things are approaching hospital stage we'll call my MIL to come over and stay with our son.
I'm uncomfortable with potentially laboring without anyone there to watch DS in the event things go quickly. All my people are comfortable with my birth plans and experienced with laboring at home for long periods of time. I figure at the very worst I don't get through my whole list of folks and whoever I'm with hauls DS and I to the hospital and DH meets us there.