If you're too far from there, you might wanna get a seat nearby to them. If there is relatively long distance between your seats, you will have to raise your voice and talking in high voice might damage your vocal chords. Also, it might imply that you really wanna join this conversation.

If you're near to their seats, then it's good. Now you just have to pick a conversation subject which you can contribute to. You just need to start conversation in a polite way without showing any eagerness to join it.