I use 2 methods of working between my 3 machines.
I have an upstairs Studio DAW where I do my recording, a Downstairs editing and mastering DAW and a laptop.
Method 1- external 1TB HD
Method 2- a cloud service- One Drive.
All my projects are in their own folders and those folders are inside an "album" folder.
On all machines I have a Sonar Data drive ( partition on my laptop) and Sonar is set to "open" there looking for Projects.
So all I need to do is drag and drop my project folders to the External drive or save as to One Drive.
Then drag and drop those to the second machines Sonar Data Drive.
When I do this I often date the Folder so as to keep track of where my most up to date stuff is. This is were One Drive is better. as everything is automatically in sync.
I always use the FILE menu for opening projects. I set Sonars Pathways to go directly to my Data drive.
When you open those projects they should be more or less identical to the versions on your other machine.
What's important is to have all the same VST's and Plug ins. My 2 desktops have everything loaded and licenced.
Another thing is to have 2 similar audio interfaces or use the same one for both. Using a radically different interface, or worse, none at al,l upsets Sonar and you'll have a bunch of dialog box warnings happening.
My 2 interfaces work without issue and the projects open on both computers with out a hiccup.
I set up the downstairs DAW so as not to abandon my wife at night. It's in a family room. She's used to hearing the same song over and over :) I don't record, I only edit stuff and experiment with VST's and plug ins.
So instead of the external drive I thought I'd use One drive. Works like a charm. No more worries about which is the newest version.
It also gives me an off site back up of my work.
I did learn not to try and record audio directly to one drive. It crashes. I use "save as" to create a local file and use that. When done I just use "save as" again to one drive.
I am going to set up an on site shared Hard drive via my router and CAT 5 system someday.
If your projects are not properly stored in one folder then you can easily fix this by opening them one at a time and using "save as" to the external drive and make sure to tick the "copy audio with project" box.