I've never physically separated my dogs.
I simply stand and step in as needed. With meals, I would make both sit and wait, then put the bowls down and release the dogs. I put the bowls about 2-3 feet apart (the width of my kitchen aisle). Often the more food oriented one (or puppy) would try to check out the others bowl. I would just keep redirecting them to their own bowl. They learn that they aren't to eat out of the other bowl.
With my prior two dogs, Moose-dog was a VERY slow eater and Bat-dog was an inhaler. I taught Bat-dog that she could not check out Moose-dog's bowl until I said OK. She would eat hers quickly, then sit and watch in anticipation like a kid at Christmas while he ate kibble by kibble by kibble. Once he was done, I gave her the signal and she would clean the bowl. Sometimes he left a few kibbles for her.
With Cat-dog and Tornado-dog, they have the same meal drive and insist on sharing their bowls - so I just let them.
With treats, I do the same thing. I make them sit, then give the treat and then stop the one from going after his sibling's treat. If they eat the treats at about the same speed, they learn pretty quickly to focus on their own treat.
If one eats significantly faster than the other, then I only give "quick eating" treats. And have the faster eater play with me until the slower eater is done with their treat.
With Cat-dog and Tornado-dog, Cat-dog will only eat dog biscuits and only when she's under the bed - so I could give Tornado-dog a chew for teething without issue. When I give Cat-dog a biscuit, I give Tornado-dog one. He eats his very fast, so once he's done with the biscuit, he gets a dentastix (she doesn't like them). By the time he's eaten both, she's just about eaten her biscuit. He never bothers her for it.