I think he is just going through growing-pains... which encompasses emotions as well. Not just physical aspects.
Try helping him learn how to communicate, the "names" for feelings, that it is okay to feel grumpy but to tell you, tones of voice,
At this age, their "emotions" are developing as well... and they don't yet know how to manage it nor understand it, literally. They may not even know how they feel either. Thus, hot and cold reactions.
Try not scolding... though I know its hard. But have boundaries. Explaining what is "right" and "wrong." Acceptable and not. Manners.
Give him simple chores he can do... (not expecting him to do it "perfectly"), but the point being that he feel important and that he is "helping" and it makes people happy. Then praise him for just trying.
And, when he does something blatantly wrong or mean, on purpose... do not allow it. Take him away from the scene, or you take yourself away... say that is not allowed. Tell him he can "redo" his actions or tone of voice... give him a chance to "redo" it. Then wait. He may tantrum, but tell him to "redo" it. This teaches them OTHER ways of behaving. Or give him options.... "that was not nice. It was mean. How can you do it nicer?"
Kids sometimes act like this as well, because it gives them attention. Even though it is negative attention.
Does he perhaps feel in his brother's shadow? Maybe he gets frustrated, or feels something is unfair??? So he retaliates....
Teach him that he is a PART of the family.... and that you are all a "team." Kids need to learn that... to cooperate and help.
Plus he does not seem ready for potty training. He may be rebelling with the whole "expectations" upon him. He is DIFFERENT from his brother.
What works for one child, will not always work for the other.
My Daughter, sometimes acts up... but it is when she actually needs MORE OF ME. And just one on one with ME only. So I spend time with her... I have come to know her cues and needs. Then like a switch, she feels better. She just has to connect with me in different ways, than her brother. I just spend time with her, talking story and involving myself in her interests and what she wants to just vent about. And I don't spend time lecturing her or nagging her about anything at these moments. I just accept her. It makes her feel better.
Understand that he is not pushing you away... but that you are the closest one to him, so he takes it out on you... but actually he needs you just as much as he pushes you away. He just can't express it, properly yet.
All the best,
Susan