скажите пж правильно ли я написал?
1)my grandad often wathes the news because it's interesting
2)my granny never watches horror films because it's scary
3)my grandparents often watch TV series because it's interesting

Не правильно. Вместо  it's  поставьте they are (в обоих случаях). Т.к news и series во мн.числе.