I need to know the easiest way to share two usb printers with two
computers (which hubs,
cables etc. do we need?)

You have two USB printers and you wish to share them between two PCs. 
I am assuming you have Internet access that you are already sharing
between the two PCs via a home network.  Assuming that is the case, I
would suggest you purchase a print server from any of the well known
consumer networking companies like D-Link or Linksys (Cisco).  Each
has products that provide two USB interfaces and you can allow
printing from each of your home-network connected PC's.

both computers are currently connected to a router, with no space to
spare. How can we do this with USB hubs? It's also possible if we have
to use an A / B type box as both computers will not need to print at
once (hopefully) NOTE: this is in an office, not a home.

what dnegrp-ga means is a network "print server". This is a device
which will connect to your existing network and act as if it's a
separate computer. It then in turn have one or more usb interfaces
which connects to your usb printers. Every time you print you send the
print job to the print server it translates the job from the network
into "usb language" your printer understands. The print server
thereotically should be always on and should be able to handle
requests from both comptuers at once. USB hubs are not necessary but
if you have ran out of space on your router you could consider buying
a switch or hub and connect that to your router to provide more
sockets.