I ride with 2 on the back, and still have room to pull a trailer but I don't recommend it. It is challenging to ride with two on the back, I can't imagine what the trailer would add to the situation.
I also don't recommend putting two on the back with an additional front mounted childseat. When you have two on the back, you need to be able to get down off the bike easily, and having a child there will infringe on that space I find I really need.
I've given it some thought and recommend against doing it on two wheels. Unless you pick a completely different vehicle which has been made specifically for the number of riders and weight. I've seen such things out there... someone's trying to sell their ped-taxi right now, that would probably fit the bill. Heck, maybe you and the wife should get busy, there's a 10 person trike out there too...
