Does the eldest brother have authority or rights over his siblings in the presence or absence of parents?

If "right" refers to maintaining kinship ties and showing respect, then it is obligatory at all times. However, if it refers to guardianship (wilayah) and managing affairs, then there is a distinction: An brother has guardianship over his sisters in marriage if the father, grandfather, and son have died. But an brother has no guardianship over his siblings' wealth whatsoever. Guardianship over wealth belongs to the father, then his executor; if he did not appoint an executor, then the grandfather, then the judge.