Simeon Ebanks, aged 25 from Clinton Street, Winson Green, and Shani Ebanks, 27, from Maria Drive, West Bromwich, have been jailed for 13 and 12 years respectively after being found guilty of robbery.
The first incident happened on Wednesday 14 September at Summerfield Post Office, Dudley Road, Winson Green. The brothers threatened the cash-in-transit deliveryman with a knife and stole £26,000 cash in a security box.
Eight days later the same pair robbed another cash-in-transit driver as he was carrying a security box containing £21,000 into the Kingstanding Circle Post Office on Thursday 22 September.
No one was hurt during either incident.
The brothers made off from the second robbery in a blue Ford Focus which was later discovered to be stolen. They were seen using a sledgehammer to smash open the security cashbox in nearby Netherhouse Close, Kingstanding. They then got into a black Peugeot 206 and left.
Police were called and discovered the abandoned Ford Focus; the passenger door was open and a trail of purple dye led to a cash box and a plastic bag containing stamps.
Shani Ebanks’s black Peugeot 206 was found shortly after parked outside Simeon’s home in Winson Green. Officers discovered the distinctive purple security dye on one of the doors and inside on a car mat.
More evidence was found inside including a bandana and a large sledgehammer stained with purple dye.
Following two months of extensive detective work, officers were able to arrest and charge the brothers with robbery.
The pair denied the offences and went on trial at Birmingham Crown Court last month.
But after a two week trial they were both found guilty by a jury.
Detective Constable Max Gebhard, from the Force Priorities Team, said: “What we have here is a highly-organised duo who were professional in the execution of these robberies.
“They had made extensive plans to try and cover their tracks; both wore masks, they obtained new mobile phones and changed their clothing and footwear.
“Their actions left both deliverymen and other staff extremely shaken and distressed.
“We always relentlessly pursue offenders and work closely with the cash-in-transit industry to prevent robberies on this scale and to keep the people who work in this field safe."