I'm sure there are Skellefteå and Mora fans on here in a better position to talk about these players than I am, but these are my thoughts on these players based on what I've seen from their play with national teams:
Granberg is an outright stay-at-home defenceman with very limited offensive upside, he is a very fine defensive player however and received praise for his performance in the World Championships during the spring (that he made the team at his age despite having missed most of the regular season with injury is a feat in itself), I doubt that he'll ever crack 20 points in the NHL but he could become a very good defensive specialist. He'll probably get himself a cup of coffee with the Leafs at some point this season, if his adoption to North American hockey goes well I could see hom as a 6th/7th defenceman on the Leafs in 14/15.
Tom Nilsson is also a primarily defensive defenceman, he's not the biggest guy but he absolutely loves to hit, he doesn't quite have the same defensive upside as Granberg but on the other hand he could develop a better offensive game. Best-case scenario I see him becoming an Alexei Yemelin-like defender, a primarily defensive, heavy-hitting #4/5 guy capable of chipping in with some offensive contributions. Barring a major break-out year I'd say he is at least 3 seasons away from playing full-time in the NHL.
I've only seen a few periods worth of Andreas Johnson so I can't really say much about him other than that he has good hockey pedigree, his father Jonas was a very good SEL player for a long time.