If the maps you want to play are DLC, then they will either have to buy the Season Pass or buy each pack individually (which is more expensive). However you can still play multiplayer together even if some freinds don't have them. You will be restricted to those you all share (i.e. at present you would get a message saying Freefall is disabled becuase player X has not got it).
It is as RustyRat63 said, they will need to purchase the Season Pass (or maps) in order to play the maps online with you. Some people say that you can share the season pass if your playing split screen on the same console. However, we recommend everyone having their own season pass so that it does not lead to complications with the users account in the future.