Avast and Virtual Machines

I am using a VMware virtual machine on a Windows 8.1 machine with Avast Internet Security antivirus installed, with Hardened mode (aggressive) enabled.
I have not installed any antivirus on the guest OS (Windows 10 Preview), but I received Avast reputation warnings about files I downloaded inside Windows 10.
Looks like Avast “Hardened Mode” checks file downloads in the guest OS too. Nice.

But, my question is: can I (should I?) install Avast on the guest OS, and with what settings?
Will the two Avast instances (on host OS and guest OS) interfere with each other?

I installed Avast on my windows 10 VM (VMWare) and it plays quite nicely