Question: As 4 boys and 1 girl are going to head to Iran, will it be acceptable to share hotel rooms and sleeper carriages even though we're all just friends?
I have also been trying to find flights from Shiraz to Kish and back to Tehran.

Answer: It is not forbidden for the foreigner citizens to share a room even if they are not married.
You can also check http://www.uppersia.com/Iran-transport-services/iran-flight-ticket-booking-service.html for the flight booking.

Check the cheapest Iran tours at http://www.uppersia.com/Iran-tours