I like to use the acronyms DOCTOR (ser) and PLACE (estar) for this.
DOCTOR stands for:
Description, Origin, Characteristic, Time, Occupation, and Relationship
PLACE stands for:
Position, Location, Attitude, Condition, and Emotion
The answers would be:
3) están - Attitude
4) es - Relationship
5) está - Condition
6) está - Emotion
7) está - Present Progressive (estar + verb with -ando or -iendo ending)
8) está - Present Progressive
9) está - Present Progressive
10) está - Attitude
11) eres - Characteristic
12) eres - Time
Hope this helps :)
