Shaxx could be from an older time period since he eats haggis which probably was too common during the golden age or even modern times. I imagine that Osiris is ment to be an ancient Egyptian. As far as reviving other guardians, its hinted at that Shin malphure died as a baby then was resurrected by a ghost before it sacrificed itself to save a group of pilgrims. Later Shin malphure would inherit the ghost of his mentor Jaren ward