Full-time squad member Oli Field and reserves Joe Gibbons, Joe Hird and Mackenzie Turner are set to make their debut for the new club at home to Rochdale Hornets on Sunday.
The four, who are all 19, will also be available for Cornwall's game at Hunslet a week later.
Loose-forward Field, son of former Rhinos and Wakefield forward Jamie Field, was in Leeds’ initial squad for last Friday's Betfred Super League clash with Hull KR.
Gibbons - a second-rower - is also the son of a former Leeds Super League player, Dave Gibbons.
Hird is a prop who has captained Rhinos' reserves this year and Turner is a winger.
Rhinos' reserves fixture at Wakefield Trinity on Saturday was postponed and they are without a fixture until a derby against Castleford Tigers at Lock Lane on Saturday, May 14.
Cornwall are coached by former Dewsbury boss Neil Kelly.