Writing for the Sunday Times, Souness says the pair are the best young players at the club.
Souness wrote: "I've pushed it to pick two prospects from Carlo Ancelotti's side.
"Calvert-Lewin looks and moves like a top footballer.
"He's a wonderful athlete, it's just whether he develops that cuteness and sixth sense to be in the right place at the right time.
"I'm also interested to see where Holgate ends up playing. He can read the game, is good on the ball and can play midfield, full back or centre back.
"Steve Nicol, my former Liverpool team-mate, was wonderful in every position he played."