1) Sandra was rummaging through the back seat when her sister saw the thing so she didn't see it herself.
2) Luck. And ugly people exist so I'm not sure why you think an ugly actress is notable.
3) Because the author said so. That's how fiction works. Now if you were to ask why a video will kill you but not seeing through a piece of clothing I'd have no idea.
4) They had a pretty big garden. There's a scene of them taking care of it.
5) She was swinging around and got lucky. And as has been mentioned, you're not 100% blinded by a piece of fabric.
6) That guy Doug's wife starts talking to her mom before she steps into the burning car so presumably from the start.
7) Blindfolds don't keep you completely blind. Plus they were walking toward the sound of the birds, which they guy on the radio told them to do.
8) They also have a garden, but who cares? We only were in there for like 2 minutes. Might as well ask how they keep it sanitary with no bathrooms or where they sleep with no beds.
9) She thought they were going to die and didn't want to get attached to them. She realized that she was wrong and by the end of the movie she is convinced to give them names.