Well, if be honest, it's not a trivial task
Firts thing that comes to my mind is to implement timer , which will be every 2 or 5 seconds gather neccessary information and synchronize your table data.
But in this approach there are a lot of pitfalls, which needs to be workarounded.
Do you eligible to change the data (structure of db)?
In case of yes, i could advise to you, to create a utility table in db , and log all action to that table:
for example at 15:35 user A(PC1) add one row , when timer callback will be invoked it gather all data from that table by specified period of time and performs synchronization.
But this approach also not so smooth, as it requires a lot of query to DB...
Another one, which is more convenient (for my opinion!!!) is to do all kind of this stuff via SignalR framework, if you need more detail about that, let me know and i'll cover it!