Do the sons of Ali and Muhammad Salih have a share in the inheritance of their paternal uncle Salih, which their paternal uncle Uthman inherited in full?

If Salih passes away and has no wife or relatives except his brother Othman and his nephews (sons of his siblings), then Othman alone inherits from him, because the nephews are excluded by the presence of a full brother. It is recommended for the brother to provide for his nephews from the inheritance. Note that matters of inheritance are complex and require consulting the Sharia courts to verify all rights, debts, and bequests.