Does Probate has to be applied by two people

I want to know that grand mother have been will a land for five person, and for grant probate one person apply for grant probate. our executer also came to court for witness but judge ask why one applicant apply for probate. minimum two applycant should apply for grant probate? If one person apply for probate then how to solve this matter, we are simple person and don't know about it. plese help sir.