I am not sure about the bed wetting issue. If he is getting mad at his sister under Cocerta and was not before Concerta, maybe the dosage is too high. Talk to his doctor about decreasing it or changing to another medicine such as Metadate CD.
My son is 8 on concerta and he also wets his pants I am begining to wonder I have read the literature and can't find any connection. But I do wonder.