I've got a uplay account so does this mean that my friends that play with me must also get one or what?

This means you don't have xbox live gold membership , you will need xbox live gold membership in order to play online

or if you have any free xbox live trials like 48 hours or 14 day , use it you can access online features in those limited time

hope this helps :)

Unfortunately, like Goku369 said, it has to do with the fact that one of the people in your party does not have a valid Xbox Live Gold membership, which is needed in order to play multiplayer on most games. You'll need to purchase a subscription or ask one of your friends to see if they perhaps have a 14 day or 48 hour free subscription pass to XBL. Sorry that your fun was cut short, I hope you manage to get to play in the future! Best of luck!