My uncle is being unreasonable? How can I help fix this?

A year ago, my aunt living in HK passed away, leaving my little cousin (9 at the time) and her husband. My auntie's dying wish was for her son to come live with my family here in Canada so that he may be taken care of properly, because she knew that my uncle would not provide much care for her son. However, my uncle is unwilling to part with his son. I understand that he is the only thing left for him, but at the same time, he does nothing to help my little cousin. Ever since my auntie left us, my little cousin's grades have slipped because no one is there to watch him, so he spends his days online and watching TV also, he has gained a LOT of weight, and his father doesn't even bother to buy him clothes that fit him (right now he is wearing clothes so small that his tummy is sticking out) and he's even too lazy to hire a tutor to help my cousin. It's not that he doesn't have money either, because the money from my aunties life insurance is already enough to help him and my cousin. My mother is practically begging him to let us take my cousin so that he can live a better life before its too late, because here we can provide him with all the proper care and education, but my uncle does not budge... how can I change his mind?