Jarvis had a blank-firing pistol in his waistband and was carrying gaffer tape, leather gloves and cable ties.
Dorset Police said the two men conspired with Edwards, who also worked as an escort, to commit the robberies. Powell had a balaclava, locking knife and latex gloves. Their offences included robbery, conspiracy to commit robbery and possession of an imitation firearm.
Det Sgt Catie Holmes said: "I would like to pay tribute to the lrvel for having the confidence in Dorset Police to come forward and report the offences. Officers found Edwards was driving wearing latex gloves and a balaclava.
Detectives said the gang was caught when a police patrol stopped an Audi Q7 in Charminster Road, Bournemouth, on 20 March. Jarvis, 24, and Powell, 24, were jailed for and-a-half years, while Edwards, 51, was given a year sentence.