I don't know about being the only one to teach tricks (provided that they are using a humane method, and not indulging with fatty treats), but I do know the annoyance of seeing someone else encourage a behavior you're trying to eliminate.
I usually just address everyone altogether, instead of singling out the offender. I'll say, "Please everyone, if Ace jumps up on furniture, or looks like he would really want some of your fried lunch, don't indulge him. He is happiest when he stays out of trouble with Mommy!" No one's feelings get hurt, and the message gets through without sounding overly critical.
I feel for you, my younger son's nanny taught him to stomp on bugs, where my older son very carefully carries any bugs we find in the house outside. Made for problems sometimes. A dog (or kid) can learn to act differently around different people. My husband lets his spaniel, Jack, jump on him, where I won't tolerate it. Jack knows not to jump on me, unfortunately he will jump on guests.
I wish my family would spend more time teaching the dogs. The dogs know my hand gestures and voice and so they don't always know what others want. If your guest is teaching an acceptable trick, I would act interested and learn what they are doing, I need all the help I can get.
My mom and her husband came out to visit this past week for my son's Eagle court of honor. They had given up Dolly and I was worried how they would act around her. (My mom kept saying that I had done wonders with her and she was a different dog :). Dolly's past daddy invited her up on his lap, so I said to Dolly- "still conning people into letting you on the furniture, huh?" He put her down. I think your reaction to each family member would depend on your relationship with them and how well they would take your asking them to stop what they are doing. Sometimes just distracting them or the dog, saying it is time for the puppy to have some quiet time, or to go outside or for the adults to get out the monopoly game, or something would help.
Always beware guests. They might put an empty snack food bag into a wastebasket. That could kill your dog.