I’d be willing to bet that there is a male role model in Jr.’s life who talks to Mom/Linda in exactly the same way. A three year old doesn’t argue like that, but they can mimic someone who they consistently hear doing the same. Mom/Linda needs to set some boundaries for both these males in her life unless she’s content to be the welcome mat forever.
If you were 22 lbs. being hit by a 150 lb. person, do you think you’d get hostile? Train, don’t hit pets, you’re supposed to be smarter than your pets!