Inherited, as in their previous owners are no longer with them? This may be a sad time for the pups. Their mommy/daddy is gone, they're going to a new place, and they are going to have to re-learn everything. My friend inherited her mother's dogs when her mother and father passed away. It was an adjustment period, but they seem to be getting along just fine. The one that was really bonded to her mom is still not ok though.
It's obvious she wants nothing to do with anyone, except my friend who looks like her mom.
Anyway, just be patient. It'll take a while for them to adjust to you and your jack russel/chi mix. Have lots of patience for them.