This thread caught my interest because I'd like to know the options for a future trip, not because I have any tips. I assumed that I'd leave LAX and overnight in Europe, then continue with a connecting flight. I've done that before, and it went smoothly. I had booked LAX-FRA-JNB. We had an evening in FRA and then a bit of rest before continuing on the next morning.
I have an upcoming trip that is LAX-MAD-JNB-HKG-LAX on OneWorld. I'm thrilled to have found this award.
Of your choices, the DUB option looks interesting. You could sleep on both flights. There are lots of connections from JNB if that's an option for you For myself, I'd hate to have to double back up the planet to connect from JNB if going further north. Perhaps you share that sentiment.
I know there are less flights to NBO or JRO, but some cursory looking a month or two ago showed some decent choices on Star Alliance to NBO. Is there a reason that an EU layover isn't an option for you? Did you actually find saver space for 4? That might prove to be the deciding factor.