1. He _______ a film.

is watching

2. They _______ their mother.

are helping

3. They ________ a song.

are singing

В present continuous употребляется глагол с окончанием -ing, а перед ним должна стоять форма to be. То есть:

I - am, you - are, he,she,it - is

we, you, they - are