Stratesave can backup running virtual machines from the host through VSS. The virtual machines' .vhd-files and configuration will be backed up (full backup). To restore a single file from a guest, restore the corresponding .vhd-file from backup. Then use VHDMOUNT to mount the virtual machine's data.

Will it restore individual mailboxes?

Stratesave supports restoring Exchange Database to Recovery Storage Group or Recovery Storage Database, from where the mailboxes can be restored with ExMerge. See Exchange Server documentation for details.

Is there any way to disable the 2nd tape, because I want only one copy?

The backup rotation scheme needs at least 2 tapes, which are filled alternately. So if 1 tape goes defective, you have still the other tape. Also, when PC crashes, while backup is written to tape, you still have the previous backup available. If backup would be written always to the same tape, and PC crashes exactly during backup, there would be nothing to restore from.

If you absolutely must keep the same tape in drive, define "tolerant" mount policy. This accepts the tape in drive even if it is not the planned rotation. But again it is better data security to switch backup tapes.