First, you must address them by their name. Dad, Boys, Rocky, etc. This is so that they know that you are talking to them and not the wall. So that they know you aren't talking aloud in an effort to amuse yourself by composing poetry to the void.
Second, you must use short, simple, single-word verbal commands. Nothing too complicated or the words might lose potency and begin to sound like more poetry to the void.
For instance, you say, "Boys, stay" so the dogs know that whatever happens next they aren't supposed to move. Or you say, "Dad, look" so he knows the paper you are waving in his direction is meant for his inspection.
Now, over the years, I've taught my Dad and dogs some unusual commands. I've taught my dogs the command "Boys, smell," which means that they are allowed to smell but not eat any item I am about to present to them. And my Dad I have taught "Dad, volume," so that he knows to turn the volume down or up on the TV if it's not correct.
But it's important to remember that all dogs and Dads have limitations. There will be some tricks that you simply cannot train your dogs or Dad to do. My Dad cannot be trained to put a twist tie around the garbage bag if he takes it out. My dogs cannot be trained to not chase the cat when she runs.
There is always the chance that they will forget old commands when they are too excited to focus. Intense sports may make Dad forget what volume even means for a second or two and the presence of a leash will make my dogs forget what sit means.
But a well-trained dog is not perfect, just one that tries hard to please. A good and well-trained dog sometimes remembers the right commands, but always remembers that love comes first and the rest is simply not that important. The same goes for Dads. Nobody is perfect but love makes all the difference.
With Love to my Dad and all my dogs.