The promising youngsters are added to a squad with an average age of just 26, but despite their relative inexperience, Edinburgh are still targeting their best-ever finish of fourth spot in the Magners League.
Their arrivals strengthen the front-five department with hooker Crombie, prop Traynor and lock Turnbull all shining during the Scottish Hydro Electric Premier One season with their respective clubs.
Crombie, 21, admits 2008 has been a year of achievement; following up his Scottish Hydro Electric championship success won while playing for Boroughmuir with a professional contract.
The Kirkcaldy-born front rower said: "After winning the title with Boroughmuir and now getting the contract at Edinburgh, 2008 has been a good year, but I'm hoping next year is going to be even better.
"It is something that I've been working towards for a long time and I'm really pleased that it has now happened.
"My first aim is to challenge Andrew Kelly and Steve Lawrie to become a regular squad player and then after that I want to push Fordy (Edinburgh and Scotland hooker Ross Ford) as hard as I can.
"My time at Boroughmuir has been brilliant and helped me to develop as a player. The standard of the players around me was very high and that made it a lot easier."
Watsonians captain Traynor has been hovering on the periphery of Edinburgh's professional ranks for the past four years and made his first team debut as a replacement against the Newport Gwent Dragons in May 2006.
The 22-year-old prop paid tribute to the influence Watsonians has played in his development over the past two years.
Traynor said: "I'm thrilled to be coming on board at Edinburgh. I've been involved with the club as an apprentice for the past four years.
"I feel I've learned a lot over that period of time and now I've got a professional contract I want to prove I'm good enough to be there. Next season I want to stake a claim for a place in an Edinburgh jersey.
"If I look back to where I was a couple of years ago, I was pretty immature as a rugby player.
"But at Watsonians under Cammy Mather, who is a past internationalist, he instilled a few pointers in me that has enabled me to become a better professional. I think I'm a better rugby player now and Watsonians have helped me greatly in that aspect.
"That has stood me in great stead and the club has supported me in my quest to earn a professional contract."
Towering lock Turnbull, 21, revealed he was thrilled to be given a professional contract and that he is planning to earn a place in Edinburgh's second row next season.
He said: "I'm absolutely delighted; I've been working for it for quite a while, so to eventually get it is really good.
"I've had quite a tough season with injury this year, so hopefully next year I can get a good pre-season under my belt and push on from there. But first and foremost I just want to wear the Edinburgh shirt."
Away from rugby, former Dunblane High student Turnbull's main claim to fame is he used to play tennis against Scotland star Andy Murray.
He added: "It is a bit of a claim to fame; I used to play tennis quite a bit with him when I was younger. We went to the same school and I know him pretty well.
"It would be great if I could achieve the same success in rugby that he has achieved in tennis."
After seeing a further crop of players graduate, National Academy manager Stephen Gemmell endorsed the trio's promotion into the professional ranks.
Gemmell said: "The Academy is there to produce players for both Edinburgh and Glasgow and this is evidence that it is working.
"It is pleasing to see all three players progress through the National Academy structure into the professional game and we wish them well as they embark on to the next chapter of their careers."
Edinburgh head coach Andy Robinson welcomed the arrivals and believes that promoting homegrown, young talent is the right way forward for the team.
Robinson said: "I'm really pleased that Sean, Kyle and Steven are joining the club. I have worked closely with all three players over the course of the season and I've been hugely impressed with the potential shown.
"Their enthusiasm and hunger to learn has really stood out and their arrivals add further vitality to an already vibrant young squad."
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