Not entirely sure what your question means but if the premise is to have to 2 phones
operate on the same machine it is a simple matter of installing the appropriate OS
for each. Once you connect a device Desktop Manager will recognize each
unique PIN and you can go from there.
Yes. I was using DM4.6.17 and recently uninstalled it and downloaded DM5.01.28 and have synced all of my berries. DM5.0 will automatically download what it deems the correct os for your phone.
Just make sure you are either using different Windows profiles or different Outlook profiles. It will make your lives easier and prevent accidental deletions of those non essential contacts/events/tasks that belong to your other half but are clogging your phone.