1.1
2. they're
3. it isn't
4. that's
5. I'm not
6. you aren't
1.2
2. am
3. is
4. are
5. is
6. are
7. is, are
8. am, is
1.3
2. My brother is a teacher.
3. This house isn't very big.
4. The shops aren't open today.
5. My keys are in my bag.
6. Jenny is 18 years old.
7. You aren't very tall.