Change instance local variable through RPC to All and to one

Ok, so i have a prefab called player in a pvp game(player vs player) and i want to change the damaged (int) playerHp variable through rpc like this:

onColissionStay(col: Collision){ if(col.gameObject.tag=="player"){ //damage another player with my atack power damagePlayer(this.atackPower, col.gameObject); } }

@rpc function damagePlayer(atackpower: int, another GameObject){ //damage another network player on his Player.js.. but how? is
//realy a gameObject or networkgameobject? how to acess his hp?? }

the other issue is change one int variable SpawnOrder (must be global and same for all users) and belongs to serverScript i will increment it when a client connect... so

OnConnectedToServer(){
SpawnOrder++;//this must increase globaly, so all players connected must inscrease
//its value
spawnplayer(SpawnOrder);
}

Thank you very much!