We went to see the latest Star Trek movie.
We like to sit in the very last row of the theatre. We were the first to arrive and we took our usual seats. We watched as a family of five walked in and sat directly in front of us. Really? There was nobody else in the theatre! They could not sit at least one row in front of us. When dad and teenage daughter leaned back the back if his chair was touching my knees. My wife commented on how rude they were and we got up and re-located a few seats down.
The theatre never filled up.
As the end credits started to roll the five of them left. A few minutes later the two adults came back and were looking on the floor and between the seats, obviously they lost something. We also saw the kids looking threw the trash.
karma is such a wonderful bitch.
PanningForGold 
We went to see your niece perform ballet at the closing recital. We were first in line and took front row seats. Your sister decided we should sit in the second row so her photos wouldn’t be pointing upward as the stage was high. We moved to the second row. She decided to sit in the third row. The front row seats were taken by this time and a man with a fat head sat in front of me. That’s life. I just moved my head from side to side. She was terrific, by the way.
There are a few differences between your experience and mine. The first being in your case people want to sit up front. And you would expect a large turnout. You had to know if you chose not to sit in front but took the second row back somebody was going to take the seats in front of you.
In our situation there were hundreds of seats, the theatre was empty, they could have sat a row apart from us, they could have sat a little to the side so they were not directly in front.
You ended up having to bob and weave because you gave up your front row seats knowing the chances of somebody sitting in front of you was high.
I would not have had an issue in your situation. I would not have been annoyed in our situation had the theatre been full.