Deliberate mistake: At no time can a player on the ice play without a helmet. It may be legal in professional hockey, but never in youth league games, world championships or not (This happens when the goalie comes out of the crease and takes his mask off to shoot his "knuckle-puck", as well as the penalty shot in the first movie.)
Deliberate mistake: During the big game in Iceland, I counted about 20 charges of cross-checking, 10 of roughing, a couple of tripping and slashing and a host of others. Any referee with the brains God gave a baboon would have caught those calls.
Answer: There may be a number of reasons, but the most likely is that, if players work really well together, it makes sense to have them on the same line, regardless if they are both enforcers or not. To give an example, the 1990s Detroit Red Wings had the "Grind Line", which consisted of three forwards who were all known for their aggressive, physical style. The two wingers in particular were team enforcers. They meshed so well as a unit it wouldn't have been as effective to split them onto different lines, just to provide an enforcer to each. The combination of all three on one line worked very well, and other teams copied the format, though of course it was not unique to this team (see, for example, the Philadelphia Flyers' Legion of Doom).