You can do it with 3 or 4 Macs no problem.. they only have small disks so your TC has plenty of space..
There is WiFi in the office and want to use it this way.
Let me just make a comment on this.
You plug the TC into the office network by ethernet.. you run it in bridge mode on the network side.. that means router bridge.
And you create a wireless network.. You can use the same or a different name to the main network.. I recommend different.. and if you want to use wireless in the Mac not ethernet then use the 5ghz in the TC.. because it is faster and it will not overload your normal office wifi with backups..
The two Macs can slow your internet while they do backups.. it might only be a few minutes once an hour but it is still significant in some situations.. be prepared to fine tune your setup a bit.. and using ethernet is hugely better if this is possible.
If you have no need of the TC wireless and can setup the TC by ethernet that actually is possible even if the TC is not part of the network.