I'm not sure about your stats - how many 16/17/18 years olds play regular league football? Call it 7 seasons and you're being fairer. On soccerbase, these are there appearance stats.
Browne - 93 appearances plus 44 subs = 137 games he's been selected. So approximately 20 games a season he's been "fit" for, if you assume fit means he gets on the pitch. There are probably other matches he was sub, but not put on, so he's probably been fit for more than 20 games a season.
Edwards - 57 apperances plus 89 subs = 146 games. Similar to Browne, but with a higher number of subs appearances.
So definitely a gamble, but not necessarily two 10 game a season players. You'd also hope at 26 they are at their peak, performance, but also in theory injury wise.
It's a big decision for the club what to do with these two (and Murphy -181 appearances plus 144 subs = 325 games, over 10 years)