My dog pulls on the leash

Hi,

Our Jack Russell takes hybrid always on a leash when my husband or the grandparents with him walk. I have the feeling that our dear dog turns fully into an other dog then.

When I'm alone with you all is good and it is very good. You know exactly how it would correct , behaves correctly but only for me!

Is that a pecking order thing or a guardian instinct? I'm over my family rather a quiet guy and not as loud as my husband or the grandparents.

I would be very grateful for tips!