They had a chance of Survival
This part baffles me: When the mom walks out with the killer to greet the neighbors on the boat, she just introduces Peter/Paul and doesn't let on that anything's wrong. This was after her dog was killed and her husband clubbed. I mean, it was the one guy against herself and like 2 or 3 friends on the boat. Not to mention that he didn't have a gun or anything, and his accomplice was separated from him in the house. If it were me, I would've said "Help, this guy and his friend are attacking us!" and we could've tackled him. Then, I would've used their phone to call for help and run inside and tie up Fatty. That was her only chance to ask for help. Once you isolate yourself with a killer, you have less of a chance of survival. I don't think at that point the killers had a gun, only gulf clubs in the house. The guy was disarmed when he went outside with her; I don't get why she acted like everything was fine.
Also, how do they not know the phone number to the police? Isn't there a 911 in Austria? They took their sweet time in the house after the killers left. Just sitting there, then slowly changing clothes, then drying off the phone, blah blah blah. I mean seriously she could've run, brought the hairdryer to the husband to dry the phone and gotten the hell out of there!
This movie was definitely more realistic than other thriller/horror movies in that the guy was totally unheroic and incapacitated - it remind me of What Lies Beneath when Michelle Pfeiffer manages to save herself from drowning in the tub and drag herself out even though she had been totally numbed with no leg usage capacity. In American movies, people sure do seem to fight a hell of a lot harder for their lives. The only time this family tried to do something was when the mom grabbed the gun.