The 21-year-old Brisbane-born locks - whose mother Linda hails from Carluke in Lanarkshire - come straight from Australia's national academy programme to join the club's elite development squad and begin an eight-week pre-season campaign at Murrayfield.
Edinburgh assistant coach Stevie Scott told the club's official website: "We're delighted to welcome these two boys to the club, having identified them as hot prospects for the future through their performances in Australia's top domestic division.
"They're both very athletic and mobile, which are important attributes in the modern game.
"I'm looking forward to seeing them in training next week and helping them develop into top players for the club."
The twins have played for the Old Boys since the age of six and have gone on to represent Australia's national rugby academy against international development sides in the 2013 IRB Pacific Rugby Cup.
Alex said: "It's fantastic to be here. I'm a bit nervous but really excited to get this opportunity in the home country of my mum, who's delighted that I've come here to play rugby.
"It's good to get out of my comfort zone. I'm looking forward to working hard to get the most out of the experience, and to do myself and my family proud."
Ben added: "One of the main reasons I've come here is because I want to work hard and play hard.
"It's how you mature as a player and as a person and it's an important part of being a good second row."