Phantom Girl was made from a Gwen Stacy head (with the hair whittled down for the pig-tails), a Black Widow body, and duct tape for the baggy sleeves.

Saturn Girl was made from a Vindicator body, a Psylocke head, an a skirt from a Gwen Stacy figure.

Polar Boy was made from a Silver Surfer body, with elastic bands for the belt, cuffs, collar, etc.

Cosmic Boy was made from an Archangel body, an Ant Man head (from the Avengers animated line), and elastic bands for the cuffs.

Ultra Boy was made from a Daredevil body, and a Prime head.  The boot cuffs are made from elastic bands, and the belt and insignia are cut from a piece of ribbon.