Answer:
1. I am Marcus, and this is MY garden (possessive, first person pronoun)
2. My mother is Susan, and this is HER hat (possessive, third person feminine pronoun).
3. They are Robert and Adam, and this is THEIR bedroom (possessive, third person plural pronoun)
4. He is Marco, and this is HIS living room (possessive, third person singular masculine pronoun)
5. We are Betty and Barbra, and this is OUR favorite book (possessive, first person plural pronoun). ITS name is Twilight (possessive, third person neuter pronoun).
6. She is Rachel, and this is HER sister (possessive, third person feminine pronoun).
7. These are my teachers. THEIR names are Paul and Rita (possessive, third person plural pronoun)
8. This is my brother. HIS name is Peter (possessive, third person masculine singular pronoun).
9. We are friends. OUR hobbies are gardening and walking (possessive, first person plural pronoun).
10. I am Sophy and this is MY dog, Aladdin (possessive, first person singular pronoun).