Help with ue4 project levels

hi guys i am new to ue4 and i am having a problem with my project. so i work with two other people and they have made different sessions of the map on other PC and they are all of our projects into one project file but they are all different part of landscapes. now the problem with this is when we click the play button to run the game all of the landscapes but the one disappear. dose anyone have any idea what we are doing wrong. thanks…

-how have you put the map together?
-do you use level streaming? :slight_smile: