Payton is the son of former Blues and All Blacks first-five Carlos Spencer.
All Blacks Sevens head coach Clark Laidlaw said it's great to have the youngsters, who were all at high school last year, in the the squad.
"We are really excited about for the next couple of seasons, these three young players have lots of potential, it will be great to see them develop as rugby players but personally too on and off the field."
After making his mark in rugby league, Tito-Harris has decided to focus on rugby sevens.
