Want to give answer with details so lets assume the names:
Arjuna is a father of Drona. So he is the first father.
Drona is a father of Ram So he is the second father.
Now we have two fathers Arjuna and Drona.
Ram is a son of Drona. So he is the first Son.
Drona is a son of Arjuna So he is the second Son.
Now we have two sons Ram and Drona.
This is how we got two fathers and two Sons but in actual they are three individuals.
When everyone has got an apple each. They will have only three apples. This is how it is possible.
Short answer is Drona is a Father as well as a Son.