I train this by starting out with games. Training with games makes it more fun and easier to understand. My dogs favorite game is fetch. So I would take them outside I would tell them both to sit in a "by me" position(beside me on my left). Then I would say "Name Wait". Then I would throw the ball. and then just as I send the other on to go get teh ball I grab the collar of the one staying by my side. Then I immediately praise before they have even had a chance to get their butt off the ground. The I switch and do this with the other one. I do this about 5 times each time I play fetch with them. Till it sinks in. In a couple of weeks I can put one in a sit, down or stand and send the other to get teh ball.

For other commands I work with my husband. We each take a dog and work them first at a distance form each other(we steadily move closer though as they listen and obey) and give different commands. If we get to a distance where they ignore us for teh others command then we stay at that distance and keep working at it till we can agian start moving closer or further away. They we switch. In a few weeks we can either be side by side or distance apart, in the house or outside the house and have then listen to seperate commands. Patience is the key though.
Nicole