Here's the completed dialogue with the verbs in the Present Continuous form:
Pops: What are you doing (you / do) on Monday afternoon?
Gran: I am meeting (meet) some friends in town. We are going (go) shopping. What about you?
Pops: I am playing (play) chess with Monty. Then in the evening we are having (have) dinner at the Explorers' Club. The members are celebrating (celebrate) the club's 100th birthday!
Gran: Are Mac and Eva going (Mac and Eva / go) too?
Pops: Yes, they are. Why don't you come with us?
Gran: Good idea!