This may not be achieved in XSD 1.0: you basically want an xsd:all compositor (scroll to the xsd:all example), where containing particles can have a maxOccurs > 1.
XSD 1.0 with Schematron would work with no issues.
XSD 1.1 relaxed this limitation; if you're interested in either of the alternatives, tag the question appropriately and I'll update the answer.