4 fathers 2 grandfathers and 4 sons riddle

Can you solve this clever riddle?

4 fathers 2 grandfathers and 4 sons

Four fathers, two grandfathers and four sons went to watch a movie.

What is the minimum number of tickets they need to buy?

Four tickets for 4 people in total.

Explanation.

Two grandfathers: Each grandfather is also a son and a father. So this makes two grandfathers, two fathers and two sons.

Two fathers: Each father is also a son. So this makes two fathers and two sons.

What is easy to get into, but hard to get out of?

Trouble.