Relevant rules
Space Marine Codex p98 wrote:Fire Points: Two models may fire from the top hatch.
Okay, since Combat Squads are allowed to be in the same transport now, what happens when a tactical squad divides down into a Rhino, specifically in regards to the fire points? Which option do you feel best meets the rules?
Option A: Any two models in the tank can use the hatch. Two marines from squad A, two from squad B, or one from each.
Option B: Only one squad may use the top hatch. One or two marines from squad A OR B, but not one from each.
Option C: Up to two models from EACH squad may fire from the top hatch.
Option D: Other