If you did what I understand then you should already have xml files for each machine in libvirt notation - correct?
If this is the case you can simply use the uvmm command line tool to define it:
univention-virtual-machine-manager define uri file_or_xml
Please also see the man-page:
If you only have the qcow2-image then you need a “domain definition” (see the mentioned libvirt xml format). I would recommend to create a dummy machine with the UI and then have a look at how the xml files should look like (this has to be done on the virtualization node, in case if you have seperated the management node and the virtualization nodes):
virsh dumpxml instancename > instance.xml