Sync via USB flash drive with changes only

[chris.10801080]

Can FreeFileSync work for the following situtation?

Situation:

Let's say I have 2 computers, A & B. And each has a root folder, whose contents I want to keep in sync - via a USB flash drive. So, User A is making changes on Computer A, and User B is making changes on Computer B. And somehow, a USB drive can be passed back and forth between them, in order to keep their files in sync.

Also, it's possible that User A & User B edit the same file before a sync occurs - so when the sync occurs, maybe there is some kind of warning, or options for the syncher about what he wants to do, or some kind of visual editor that allows for comparing/merging/editing of the conflicted file.

Also, I don't want all of the data to be stored on the USB drive - only the changes - or something like that - in order to keep the total data size on the flash drive low.

Can I do this with FreeFileSync? If so, how?
And if so, how would I do this with more than 2 computers (if this is not already obvious by your answers above)?

Thanks.