What is the ruling of the religion and Sharia on the aforementioned inheritance case, and on the fraud and abuse committed therein?

It is not permissible for your sister's children to seize your land unjustly, nor is it permissible for your brother to assist them in this while knowing the truth. You should try to reach an understanding with them by seeking mediation from sensible people. Otherwise, you have the right to take the matter to the courts to remove the injustice.