Is it permissible to eat from the money of an uncle whom some heirs claim took their inheritance through forgery, while he claims his grandfather wrote it to him? And is it permissible to accept gifts or Eidiya from him?

Accepting a gift from one's paternal uncle and benefiting from his wealth is permissible, even if you are certain that some of his wealth is ill-gotten, as long as he possesses lawful wealth from which he spends. However, if all of his wealth is unlawful, or if he gives you something from the very substance of unlawful wealth, then it is not permissible to benefit from it.