Two dogs form a pack and a pack is much stronger and more confident than one dog alone. Since you are not providing much in the way of entertainment at home, they might as well take themselves off and have a jolly good time fulfilling their natural hunting behaviours in the woods and fields!
Now that they have been rewarded in this way, it will be really difficult to stop them, particularly if the daughter has grown up playing games with her mother rather than you.
So the first thing to do is create a new impenetrable barrier around the garden, remembering, of course, that Jack Russells like to dig. Then you can work on teaching them to have fun with games with you instead. Get some good squeaky toys and separate the two dogs so you can play with each independently. Try to make the games as exciting as if they were catching mice and rabbits in the fields. Sometimes tying a toy to a springy stick can help you simulate the action of little prey animals as you run it through some long