Using purchased modules

Hello! I'm very new to this site, I literally just joined today. I'm running the Tyranny of Dragons campaign as DM, and I already purchased the modules from B&N. One of my players lives in Canada, and cannot always make it to our weekly sessions. If I wanted to run our campaign through this app, would I need to purchase the modules again, or is there a way to "redeem" them of sorts. The WOTC already got my $60 for purchasing it, do I have to give them even more?

Unfortunately you would need to purchase the module again.  This is due to the amount of time it takes the Roll20 team to set it up, saving you the effort.

Or you can do all the work yourself. Many members do that if they have purchased the module elsewhere. As you are not a subscriber, you would not have access to the additional features that are tied to specific subscriptions.

If I buy the module on Roll20, do all the players need it as well?

Only the games creator needs to have purchased the module... they don't even have to be the DM!