It's a zoo around here. I found there is only one safe place for the baby if I need to do something else besides hold him and monitor to make sure his sisters don't torture him.
I prop him up in bed on the Bumpo, spin the mobile, and turn on some jungle sounds from his super cool, white-noise Giraffe. This usually gives me about 5-10 minutes of time. And the girls think he is in his room sleeping, so they leave him alone. Usually.
On this day he actually fell asleep in his crib. I didn't notice for at least half an hour. I won't call the poor little guy neglected, just self sufficient.