Toddler behavior

My younger brother (age 4) is extremely defiant and extremely rude to our grandmother, he rolls his eyes and talks back all the time, I’m not sure how to handle it (I have a kid on the way so I would also like to know how to deal with this for the future) I’ve tried talking to him, he looks away and refuses to respond, I’ve tried discipline such as time out or taking things away it doesn’t work either, I’ve tried to ask him what’s wrong or why he feels the need to respond the way he does and once again he refuses to answer..