_Validate XML Schema Assertion - CA API Gateway - 8.3 - CA Wiki
You have an error in that schema import. You can't have two schemas for the same namespace, and you do in your sample. They EACH must have unique namespaces.
This has very specific tooling for imported schemas, but it doesn't process relative links either.
You need to change them to unique namespaces with absolute links. Otherwise, especially if you load that schema for a file, how will it know where to find the xsd file?
Alternately, you can import all of the imports FIRST using manage global resources, then it should use them directly, but solve the ambiguity first, or change them into includes, not imports.