Réponse:
1 - Mary's hat (le chapeau de mary)
2 - the children's teacher (le professeur des enfants)
3 - my grandparents's house
4 - Nicolas's tshirt
5 - the 2 sisters's favorite song
1 - our (notre)
2 - their (leur)
3 - his (son)
4 - my (mon)
5 - her (sa/ses)
6 - their
Je pense que tu peux continuer, bon courage