What do you do with the neutral wire of a 14/3 romex when the two hot wires are circuits for the bedrooms?

I bought four Fault Protectin Breakers for my four bedroom circuits but when I went to install them I noticed they were run with 14/3.

Each Fault Protection Breaker has a neutral pig tail built into it to land in the neutral buss bar. You are suppose to take the neutral from the homerun directly to the breaker neutral terminal.

But I only have one neutral for two circuits.

You need to find the Cutler Hammer arc fault breaker specifically made for multiwire circuits. Otherwise, you'll have to redo the circuit with 2 homeruns.