Derp, about making your character more indepth, something that might help is a summary of his time with the mercenaries till now, maybe a specific story from that time, for example how his subtle nature once aided the band on a mission, how his love of women and drink placed him in trouble or how his fear of his brother has influenced meetings with members of nobility or knights. So far you have given us his origin story, but things have happened since then. Events that shaped him from a man who only ever really brawled to one who could be relied upon in serious battle by his comrades. Since this RP is for a large part about the mercenaries, you should try to establish your role within the mercenaries more clearly. If you were a fresh recruit, your history would work, but your character is old and thus implied to be more of a veteran.

Adding more depth to his personality and skills would probably help too. For example what topics anger him. The mercenaries will undoubtedly already have come across some of them already, with bad results, so tripping people up with that would be unfitting. Also whether his respect toward authority would prevent him voicing his outrage at those topics or not. How he is calculating should probably also be pointed out. Does he just not let emotions influence his decisions or is he calculating in other ways, always looking for escape routes and scape goats, no matter the situation or something like that? This can also be worked into his skills, naturally stealthy can mean, in my opinion, two things. Either being able to sneak well and having a good instincts for creaking floorboards and such or being unremarkable, forgettable. Sharp mind comes back to what I said about calculating, specify in what way he is sharp minded. What mental skills does this apply to? Social situations? Scouting? Both of these take a sharp mind, quick to notice things that seem strange, but they are still completely different fields. On that note, he spent a lot of time brawling, so does he have a reputation? Could he come to an underground fighting tournament and get recognized as "Theo the Dirty Drunk" or whatever?

There are a lot of questions one can raise about characters. Most of these will remain unanswered in the CS and most of those again may never come up, but make use of these things nonetheless. Every little piece of trivia can add to the depth of your character and be used by others in the RP. If you do not note how Theo acts drunk, people will be a lot less likely to have their characters note his tendency to dance on top of defeated opponents while singing nursery rhymes.