Hello,
1) Sorting
you can sort list of VMs by any attribute you can find in Attritube list ("Edit widget" -> "Query" tab, "Pick sort field..." menu):
The most similar attributes are vm.volSummary.freeSpacePercentage (average free space across all disks) or vm.vol.freeSpacePercentage (free space of all disk volumes). It's not possible to show just free space of particular disk volumes in the widget.
2) Excluding particular drives
in alerts you can skip particular disk drives (unable to do that in widgets). Such issue was already discussed at Re: Skip certain volume label or drive letter in the Guest Storage Space Utilization script or Re: Re: How can I exclude a volume from alerting about low disk space? Thwack threads.
If you need to exclude particular disks on particular virtual machines then you can use something like that (this xPath excludes C:\ mount point on "tex-2k8-2LUNS" virtual machine and /boot mount point on "Analytics VM" virtual machine):
if (/virtualMachine[name="tex-2k8-2LUNS"])
then min(/virtualMachine/diskVolume[mountPoint != "C:\"]/freeSpacePercentage)
else if (/virtualMachine[name="Analytics VM"])
then min(/virtualMachine/diskVolume[mountPoint != "/boot"]/freeSpacePercentage)
else min(/virtualMachine/diskVolume/freeSpacePercentage)
Let me know if you have any other questions.