I'm not really understanding your question.
What exactly is it about the Virtual Machines you want to share?
The normal way virtual machines work is you have the VM software (in this case VirtualBox), and you can create as many instances of virtual operating systems as you can fit on your hard drive if you want (although chances are your machine will have a limit as to how many VMs it can run at once). You can have a virtual Windows install, a virtual Sabayon install, a virtual debian install...any OS that VirtualBox supports, and you can run them at the same time on your host box (in this case you stated the host is Sabayon). The VMs don't all need to be running the same kernel.
Also, VirtualBox has some options whenever you create a VM, specifically dynamic hard disk space vs static hard disk space. If you are planning on trying to link anything from one VM to the other, I'm thinking you definitely won't be able to do this with dynamic.
That said, you would probably get more/better support on the VirtualBox forums, as this is a fairly nonstandard question. The solution should be distro independent.