VirtualBox (recently or for longer, not sure) supports ova’s that include multiple VMs to be imported.
KVM libvirt.xz files should also be easily available as a single download containing both VMs.
Work has started towards a unified Whonix download rather than separate Whonix-Gateway / Whonix-Workstation download.
This will increase usability by simplifying instructions for download, verification and VM import.
Not yet tested.