Here is the completed dialogue with the correct forms of the Present Continuous:
George: Hi, Mum. What are you doing (you / do)?
Mum: I am making (make) dinner at the moment.
George: I'm at David's. We are watching (watch) the football. Is Harry there?
Mum: Yes, he is. He is helping (help).
Dad in the garden. They are watering (water) the plants.
George: Can I speak to him? He isn't answering (not answer) his mobile.
Mum: Yes, of course. Harry! HARRY! Are you coming (you / come)?