Yeah you shouldn’t work on the same file at the same time. If you want to work on the same file you should use something like a screen-share program and have only one person commit.
SVN is supported by the Unreal Editor. You connect to source control using the “Subversion” option. Then you will have to “check out” the files you are modifying. This ensures nobody modifies the files while you are modifying them. Once you commit the files anyone can get the new ones and check the files out for modification again.