Choose the sentences which are correct. You will lose points for choosing sentences which are incorrect

Choose the sentences which are correct. You will lose points for choosing sentences which are incorrect.
These are our childs, Luca and Antonella.
I'm French. My family is from Paris.
That watch is expensive.
My grandmother's 90. Their name is Esme.
That's Mark's phone.
This is my office
He's a doctor. His job's not easy!
It's our teacher birthday today.
Those singers are good.
It's a big countries.
Here are your bags.
My sister's umbrella is blue.
We're students. Your university is in Istanbul.
Is this your sunglasses?
I have a pen . My pen is black