Do you have to be there to watch both movies what if your only interested in seeing one and it’s the second showing movie on that screen are you still able to get a spot

You don't have to watch both, there should be spots. I never see it packed and lots of people leave after the first one.

No you do not need to see both movies if you do not wish to, many people only stay for one or arrive for one movie. There is a time interval between the 1st movie ending and the 2nd movie starting when many leave or arrive so it is still possible to get a spot