Click to open a project from studio pro and select the branch line from team server, if you don’t see you could refresh.
Once you open the branch line it will create a local copy of your as well. You can’t toggle between this branch line and other branch. You should close the project and open another project in same studio pro or open another new studio pro app and open you other project. That way you could Alt + Tab between two different lines of project.
Your team members need to commit changes to Team Server every time to update to code and clear the conflicts if working on the same things.
Then there must be something strange going on. What happens when you view this branch with Tortoise SVN? Assumption is that you are using the Mendix SVN and not one of your own. Is that branch visible there? And if one of the others creates a branch is that visible for that other person that created the problamatic branch?