Sometimes dogs eat their poop because the food you are feeding them is lacking in nutrients. Sometimes they eat their own poop because it is instinctive and they have to be taught that it is not acceptable. Make sure you are feeding your pup good quality food. If Jasper eats his poop - gently say no and then praise when he stops.

As far as the other dogs getting along. Make sure you do not let the dogs be together unless they are fully supervised. Then for good behavior (being in the room together nicely) - praise and treat. Bad behavior - any growling (time outs in a crate or another room). Remember a new puppy can be a little overwhelming to an older dog. Their life has changed and they can get stressed over it.