1) Don't look into things too much... nobody knows and thats how they want it
2) Billy and Stu are crazy (phsycopathic) there doesn't need to be a motive. Basically because they felt like it
3) Once again your not supposed to know for sure, they like to leave some mysteries and hope people won't look too far into it.
4) Most likely stu although billy might have used his single phone call as he said he called his dad but the sheriff already had. Once again refer to the answer of question 1.
5) I know its repetitive but refer to the answer of question 1.
6) 'Last answer'
7) Who - Last answer. Why - coz billy and stu are psychotic, they like killing. There is no rational explanations to the actions of a psycho.
8) Think so because stu is with everyone else and billy seems to come from the side of the house where the garage is when he comes to the front door. But once again we are not supposed to know these things and looking too deep into them just defeats the point of the excitement that comes with horror films (or all films for that matter)
9) They probably wouldn't have happened if all went according to plan
10) Maybe he did. As i said they are psycho.
12) Think so.
Hope i could've been of help. Sorry to repeat so much but things like that should just be overlooked because sometimes you'll find the film might not even make sense and cause you to lose your respect for the film.
Randy: never, ever, ever under any circumstances say, "I'll be right back." Because you won't be back.
Stu: I'm gettin' another beer, you want one?
Randy: Yeah, sure.
Stu: I'll be right back!