The correct answer to this open question is the following.
Although you did not attach options, we can say the following.
When a ball is popped up and caught by an outfielder, a runner at third must tag up if he/she wants to advance to home and score with less than 2 outs.
Yes, commonly, a runner can tag up in the case of a fly ball, and does not matter where the other player fields or catches the ball. Of course, if the fielder cannot catch the ball, the runner on the third base can run and score. And yes, if there are other runners on the first and second bases, they can opt to run to the next base.