help my dogs are attacking the older dog

i recently purchased a jack russell puppy she is 4 moths old i already had 2 other dogs the pup and one of the original dogs are ganging up on my maltese terrier and the other night i found her with bite marks and bleeding i didnt see it happen but ithink they attacked her i now keep the puppy and the maltese locked up and let out one at a time with the other dog sadly i am feeling i have to get rid of the puppy any suggestions?

The first thing I'd do is a complete medical workup (bloodwork, urinalysis, physical exam, etc.) on the older dog - I've heard of several situations where dogs ganged up on an older member because they were sick.

I agree with the medical work up.

What does the breeder of your JRT say? What are the lines like?

I have an old Kees who has a tumor and is going senile. His also-old girlfriend and our new, younger dog gang up on the Kees all the time. We rotate the dogs so the old timer can live his last months in peace.