When you assign a PF to a VM, it becomes VF. With SR-IOV enabled, the VM's are natively (directly) accessing resources within the Ethernet Controller via VF, while at the same time the Physical Function also has its own resources and can be used for other functions, such as emulated path.
Once you assign a PF to a VM, it becomes your VF. So you cannot further assign a PF to your VM.
With regards to the bandwidth for the VF's and PF's, it doesn't necessarily divide the bandwidth into equal portions.
For more information, you may refer to the SR-IOV Primer available on our website.
See page 12 - SR-IOV and Sharing
If you have further questions, feel free to reply to us.