What you describe I don't think is normal child behaviour, even for a 3 year old. I think this child needs therapy. I think he is in deep deep trouble if he continues this way,and his sister is too. He has suffered trauma I think, from being basically abandoned by his parents, and if they are meth addicts, it's possible he was affected by the meth in utero himself. I don't know about that... just guessing. I think this child needs help. Boundaries, yes, but he needs professional help in my opinion.