This year we are touring with 1 tandem, 1 Burley Piccolo trail a bike, and 1 single and a kid-trailer and our two boys.
Next year, most likely, we'll be ordering tandem #2.
We find the Piccolo very stable albeit a little long when pulled behind the tandem. We felt that having two tandems eventually would be more flexible than a triple now. The Piccolo is a short term, easily resellable, measure. Both my wife and I ride, so this makes the decision a little more straightforward (no, we never considered a quadruple!) since the times when only one parent is pulling the boys are limited.
Just another option. Your mileage may vary.