Validate xml against multiple xsd (which are strings)

I'm looking for a way to validate a transformed xml against a bunch of xsd-files which are loaded from database. I got 15 xsd, 10 of them share the same namespace, e.g. namespace1, 5 got other namespaces, e.g. namespace2, namespace3 and so on.

Some of the 10 xsd-files include other from that group, some also import xsds from the group of 5.

I tried three different ways to validate and all don't work as expected.

I know, that I got a working xml out of my transformation, I checked that with another tool, so I changed that default-namespace from namespace1 to namespace1'. I expect to get any error saying namespace1 expected and found namespace1' or something like that but

either I get no error (examples 1+3) or

I get an error adding the second schema from namespace1 saying "Type 'namespace1:Type.MyType' is no simple type or hasn't been declared." (but it was declared in the previously added schema) (example 2).

example1:

            foreach (DataRow dr in lstdrXSDs)
            {
                using (xsd = XmlReader.Create(new StringReader(dr.Field<string>("XSD_Content"))))
                {
                    schemas.Add(dr.Field<string>("XSD_Namespace"), xsd);
                }
            }

            XDocument xml = XDocument.Load(XmlReader.Create(new StringReader(sXML)));
            xml.Validate(schemas, (o, e) =>
            {
                sErrors += e.Message + Environment.NewLine;
            });

example2:

        XmlValidatingReader vr = new XmlValidatingReader(XmlReader.Create(new StringReader(sXML)));


        string sError = String.Empty;

        foreach (DataRow dr in lstdrXSDs)
        {
            vr.Schemas.Add(dr.Field<string>"XSD_Namespace"), XmlReader.Create(new StringReader(dr.Field<string>("XSD_Content"))));
        }

        vr.ValidationType = ValidationType.Schema;

        vr.ValidationEventHandler += new ValidationEventHandler(delegate(object sender, ValidationEventArgs args)
        {
            sError += args.Severity + "\t" + args.Message + "\n";
        });

        while(vr.Read());

example3:

        XmlReaderSettings sett = new XmlReaderSettings();
        string sError = String.Empty;

        foreach (DataRow dr in lstdrXSDs)
        {
            sett.Schemas.Add(dr.Field<string>("XSD_Namespace"), XmlReader.Create(new StringReader(dr.Field<string>("XSD_Content"))));
        }
        sett.ValidationType = ValidationType.Schema;
        sett.ValidationEventHandler += new ValidationEventHandler(delegate(object sender, ValidationEventArgs args)
        {
            sError += args.Severity + "\t" + args.Message + "\n";
        });

        XmlReader xml = XmlReader.Create(new StringReader(sXML));
        while (xml.Read()) ;