If you emigrate and then apply to the embassy to cancel your original nationality, you will have no legal relationship with your parents and brothers in China, right?

In addition, if you cancel your nationality, you will become stateless. Immigrants cannot acquire nationality (unless specially approved by the state). Canada's maple leaf card or American green card is a permanent residence permit for foreign citizens. It doesn't mean that you become a citizen of that country. If you cancel your nationality, your green card will be invalid. Unless specially approved by the state, it cannot be given to stateless persons.