Yes you need Gold to play Multiplayer with your friends. You don’t need Gold for just use the Onlineservices for Live Weather, Live traffic, Bing Mapdata, … Only if you want play Mlutliplayer with other Players, you need Gold.
But warning: The MP has a very bad bug: https://forums.flightsimulator.com/t/bug-logged-unable-to-leave-group-flight-options-greyed-out-xbox/429244/15