I think you're confusing things here. Soldiers do not get Jenova cells. Someone who qualifies for Soldier only gets one Mako bath.

The Jenova project was created to create a human-Cetra hybrid because Prof. Gast thought that Jenova was a Cetra. The project was divided into two departments from the start. Project S, led by Hojo and Project G, led by Hollander. Project S was the infusion of Jenova cells into Lucretia's child, resulting in Sephiroth and Project G was the infusion of Jenova cells into Gillian's child, resulting in Angeal.

Since Sephiroth and Angeal were classified as perfect, their cells were further researched. The humans with Sephiroth cells have become zombies. Genesis and various Genesis copies were created with the Angeal cells.

However, all G cell carriers were killed in Crisis Core. And Hojo created his own reunion theory and saw Zack as suitable for it. He only experimented with Cloud because he was with Zack.

But Zack's body refused them. And Cloud got intoxicated. So Hojo saw it as a fail. Until he realized that Cloud survived.

But that's pretty much it.