Field Hockey "referee's" are Umpires like in baseball.
There are two field umpires, each controlling roughly a third of the field and cooperating on the rest. Most tournaments and some normal matches will also have a reserve umpire who is in charge of any off-field officiating.
0 we are not playing baseball.
Two mounted umpires, and another on the sidelines.
There are 2 goal umpires, one at each end, 2 boundary umpires, one for each side of the field, and 4 field umpires. I believe some of the state leagues may have only 3 field umpires, but not 100% sure on that.
13, plus 2 umpires
Never. There are no Umpires nor are there Penalty Strokes in hockey.
2 on the pitch who make decisions based on the game and implement the rules of hockey. At the top top level, they can be assisted by numerous individuals (including Technical Directors etc) who will help with timing, implementing penalties etc.
There are 4 umpires. 2 on-field ,1 TV umpire and 1 reserve umpire...
you can have 2 teams on the ice/field/pavement in hockey.