Можно сказать this is a grandmother?

Да можно. но только если это вопрос тогда: is this a grandmother?

Да,почему же нет? чтобы точно быть уверенным,что вы не допустили ошибку,можете написать/сказать так: this is my grandmother

Hi,maria! -hello,sam! -how are you? -i am fine. and you? -i'm fine too. -what will you do this summer? -i will visit madagascar. -oh,i want to visit it too,but i can't. -why? -because this summer i will live in my grandparents. -i can to take you with me on a trip to madagascar. -really? -yes,i can. -i can't believe it. -i will go there with my cousins and parents. -i think it will be great. -we will eat some new fruits and vegetables. -i want to taste it. -we will have a funny trip. -also we can watch something films. -we can see new animals. -i will read about animals that live in madagascar. -i want to read about this too. -i should to go home. -okay, bye. -goodbye. -i will phone you.

Hi nick hi tom how are you? i am fine. what about you? me too. how long didn't we see each other? 3 years. oh! it is so long yes, it is. what do you do after school? i decided to become a policeman. but you? i am a future doctor. that is great. you will hill my wounds. ha-ha hope i won't. it seems you are not that joker that i knew. yes i am determined to become a professional doctor, so i must be serious. clear. now i need to go. would you like to drink with me tomorrow? yes i would. let's go to the bar that is near from my home? okay. goodbye goodbye