I push down then pull up on the handlebars and lean back a little to get some of the weight off the front end and over I go. There is no such thing as jump with a tandem and 40# stoker. With my single bike I would then move up off the saddle to let the rear up and over too. Watch those pedals, you can pedal a few half-strokes for momentum if need be but I like starting out with enough to begin with. Practice with increasingly larger things until perpendicular 6" is routine. When you are learning try to meet things head-on rather than at an odd angle.

Jumping something involves more speed, pushing down on the whole bike and popping up high enough to get over the something.

Bike4ever would be ever better at explaining this stuff.