if you play a player on punter does he gets points to increase his BPOS for kicker?

this brings up another question how does the postion rating go up I know playing games but is there some kinda of formule or is it just random or after so many games certainly or is that something we don't know

Each player gets a percentage chance to gain experience points. The percentage depends on the type of game: Friendlies there's a 50% chance he'll get 1 experience point and a 50% chance he won't get any experience points. For league games, it's a 75% chance he'll get 1 experience point and 25% chance he won't get any. So there's no real formula, just play the players and hope they get lucky and get the points.
As for the multiple positions, players can only gain experience points and BPOS for 1 position. Since there are two positions that cover the same 'position' (kicker and punter are both kickers for example), then it's likely that you're getting double opportunity to gain the experience points and BPOS. Not positive this is how it works, but if they are increasing much faster than your other players, it's a likely explanation.