Read Mr wibblywobbly's artillery posting with great interest

[wibblywobbly]

For a 27mhz system you would need one tx, and two boards, plus two receiver boards, plus one crystal for the tx, and two matching ones for each of the receiver boards. That way one tx would control both boards.

The IR bit will be a bit more complex, it can be done, much reading and experimenting will be required.
Controlling the turrets will mean building a turret rotation system, as you can't use servo's on an HL system.