Perhaps the easiest way to power your bicopter is to use ESCs (Electronic Speed Controllers) with a +5V, 3A linear voltage regulator, know in the RC world as a BEC (Battery Eliminator Circuit).
In fixed wing RC aircraft the ESC's 3 pin (signal, +5V and GND) BEC connector is plugged directly into the RC receiver. This powers both the receiver itself and all of the plane's servos. A flight controller usually isn't necessary.
The principle for multi-rotors including the bicopter is the same, except that a flight controller is inserted between the RC receiver and ESC/servo outputs to provide flight stability.
Power the ESCs directly from your LiPo battery and use an ESC's +5V, 3A BEC output to power your servos. Just make sure that the servo's ground return path connects directly back to the ESCs via the BEC connector and not back through your Arduino flight controller. The Arduino's GND pin should also be connected to the BEC ground.
For example, the image shows my flight controller's power bus, that's similar to the KK2s. The first ESC's BEC (signal, +5V, GND) is connected to the top row for motor 1 and powers the flight controller. The subsequent ESCs BECs are connected to motor 2, 3, 4 etc... These are attached to a separate +5V rail and allows them to power any servos that might also be required. Note that the grounds are connected together to provide a single return point back to the ESCs without passing through the flight controller itself. The PWM signals that control the ESC and servos are generated directly by the microcontroller:
Multi-rotor ESCs with BECs are becoming a bit of a rarity these days, as nowadays the voltage regulation is usually performed by a PDB (Power Distribution Board), plus the fact that most people fly smaller quads that don't require a servo (or two). However it's still possible to find them.