Good topic
When I had two adults (Charlie and Max, a neutered male Poodle - 28" and rather dominant) they did everything together - that's how they wanted it! Charlie seemed to think
"Max is my big brother - he can do anything!", while Max had decided
"Charlie is my little brother - I'll let him do anything!"
Max and Charlie would go on the same walk, but I switched-up who was 'working' and who could sniff... sometimes I had them both at heel, or both at side, or one on each, but most of the time I let at least one do anything but pull.
For clicker training I'd put one dog in another room, but any other training I'd have them in the same room so that both would be learning. I would have each practice their stays while the other worked/played. I also did some multi-dog tricks (over/under each other etc), and alternating one command each, and both responding to a single command.
They ate in their bowls right next to each other (they often decided to share from the same bowl, even if two were out). There was no need to feed them separately, though I did make sure they would eat their food in their kennels and otherwise alone so that they didn't depend on the other's presence (makes it hard to travel for shows if only one dog is coming).
Currently, since Harmony is a puppy, I've been putting her in an x-pen to watch Charlie. She has started learning to respond to commands at the same time as other dogs, but she's not ready for sit or down stays while another is moving.
My room-mates dog/s can be a little possessive of food, so I feed the puppy in her crate which also makes house-breaking easier.
For me, if I trust dogs to play together then I have already started teaching them to work together (working usually comes first, actually).
