I´m not exactly sure what you mean by "he was made prior to the Five Families being divided up". But prior to the Castellammarese war, the Five Families had already been established. The bosses were Masseria, Mineo, Reina, Schiro and Profaci. During the war, former Masseria loyalists switched sides to Maranzano´s. I guess one can argue that the New York Mafia consisted of two factions by this time (actually three because Profaci was considered neutral) but the NY Mafia was still de facto structured into five different Families.
Valachi was made into the group that supported Maranzano in late 1930 and at a time when the war was still raging. I think he was connected with the old Reina Family at the time. Although being made member of the Mafia (fully comparable to others who had been made during normal circumstances), I´m not sure that this group can be called the Maranzano Family because this group consisted of members of the Reina Family (Gagliano, Lucchese, Scillitani and others) as well as Mineo members (Mangano, Gambino, Scalise and others). They had all joined to fight Masseria but was still technically members of their old Families.
However, directly after the war, these men who had joined the "Maranzano cause" were given the choise to remain with Maranzano or go back with their original Families. Only a few stayed with Maranzano and Valachi was one them.
The Valachi switch occurred after the Maranzano killing. Gagliano and Lucchese intervened on Valachi´s behalf and saved him from being killed by Luciano and Genovese who considered Valachi as a staunch Maranzano supporter.
If memory serves me right, Valachi was given a choise to either go with Gagliano (who now led the old Reina Family) or Luciano and he chose Luciano. He was put in Genovese´s old crew, now run by Anthony Bender. This was a choise Valachi later regretted.
So from being a made member of the Maranzano forces who fought Masseria in the war, via membership in the Maranzano Family, he went to become a member of the Luciano Family.