Whilst not currently a SONOS user, am looking at getting one in the near future and while doing some research was looking at the 1 star reviews on Amazon and one on there mentioned about security on the controller app where by multiple people (in his case, kids at a New Years Eve party) could change the music on different players, so I guess the answer to your 1st question is yes, two different people can control different players.
Can't answer the 2nd question as I do not use anything Apple
Yes, multiple controllers can be connected to your Sonos system at the same time. You can play music in different rooms, contribute to a shared playlist, etc, etc, etc.
I don't think there's an option to show lyrics on the iPad app though. The metadata displays is pretty limited.