Howdy,
All Motion project files are in XML format, but they should sport a .motn extension, not .xml. I’m not sure how those files got a .xml appended to them, but try changing it to .motn and open them in Motion (assuming that they really are Motion documents).
You can also open the files up in a text editor (such as Text Edit) and check out the opening tags. Motion documents always begin with:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE ozxmlscene>
<ozml version="4.0">
In this case, the project file was from version 4 of Motion, as is noted in the ozml version.