and the twitch idk about....as for the physical thing on HIS part, when it comes to other kids, i'm one of those "if you can dish it, you can get it".....but THAT is def where his behaviour needs to come to a short and UNsweet ending!
i'm unsure if you are still monitoring this, however here are my thoughts....
there is a total lack of discipline....total....if he is "too busy" to go potty, then he needs to become "unbusy".....as in, no games, no computer etc.....as for the hamburgers thing.....it seems they only eat out, and that much meat at that age i'm sure can cause complications for his digestive and intesinal systems.....i'm country, and where i'm from, physical discipline would be in order....not beating the child, but apparently talking either doesnt help or is not used.....if it were my home, i wouldnt allow him to disrupt the enviroment, esp at dinner, nor am i a restaraunt which means he'd either eat what he gets, or enjoy some cereal ALONE.....your uncle and his wife apparently do not seem to care....it doesnt seem as if they have done anything to try and rectify his behaviour, which makes his behaviour their fault also......