J.M.
You're forgetting to factor in while they may listen to sit and stay to you, they are little and a new person (the photographer) will completely turn puppies into rebelling "toddlers"
If I were you I'd do the following.
Pick an outside setting, let the photographer pick...she probably knows awesome ones
Bring a stake with a leash to put them on for when they are not supposed ot be in the photos so they will still be contained and safe while you're not paying attention
Plan for fun candid shots of the dog and your son...them knocking him down playfully, him climbing on them, then maybe try and bribe the pups for a good photo or two but if you J. enjoy it and go with the flow the candid photos will be better
then get some of the three of you minus the pups while they are contained and bring a favorite "clean" snack and a blanekt to sit on for your son and a quiet toy for him to sit and playw ith while you get a few photos without him