wat rights do i have as first born son if another brother has named himself executor and soul bennificiary

All children have equal priority.  There are no special rights to the oldest, or to sons versus daughters.  People have the right to structure their own Wills however they want - they can give assets to charities rather than their children, one child but not another, etc.  They also can name whomever they want to serve as executor.  If you have concerns that your parent's Will was written by your brother and not what your parent wanted, you can challenge the Will in probate court.