You can put your feed in the freezer in gallon ziplocks. Take out small amounts at a time so the condensation doesn't turn it moldy.
When they are grown up your 3 chicks will need about a 50 lb bag every 2 months and if you keep it cool/dry will last that length of time. However, when they are chicks they will eat it more slowly. Feed grower feed as redsox and LoneOak said until the point of lay, at which time it is OK to switch to layer feed.
You can feed cracked corn/scratch in tiny amounts to hand tame them if you wish but they need the high protein of the grower for proper growth and development.