Jack Russell and Ducks and other pets

Question
My parents recently got a 9 week on Jack Russell from family friends. It is his second day in the house and I'm a little concerned. First, we have two other dogs. They're both chihuahuas. Toby is a 5 year old 12 pound neutered male, Mia is a 2 year old 3 pound spayed female. Both of the dogs are less than excited about the Jack Russel, Amos. When he tries to play with Mia he jumps on her back and even though hes much younger than her, he is much bigger and she is terrified. I'm not sure how to ensure that he won't hurt her and get him to calm down a little. We also have two ducks who live in the backyard. The ducks cannot fly. I am very concerned that Amos will hurt the ducks because Jack Russells have such a strong hunting instinct. Right now he seems a little scared of them, but I'm sure this won't always be the case. What can we do to make Amos' transition into our house as smooth as possible while keeping our other animals safe? Thank you for your help!

Answer
Erica, I would reinforce his fears of the ducks. Reinforcing fear is not normally something I suggest, but he needs to understand that they are off-limits. Do the ducks try to intimidate him at all, or do they run away from him?

What does Mia do when Amos tries to play with her? What about Toby?

Kristen