The problem:
2 Macs, needing to be backed up on one Drobo, Ideally using Time machine.
Q1 Is it possible to do this with Drobo share? If yes can someone please put a step by step explanation of how?
Q2 Is it possible to connect 2 macs with the Firewire 800 connections? There are two of them at the back of the Drobo…
If none of the above is possible, can someone please suggest a solution.
Many thanks,
Lionel
1 yes - possible, you’ll need to create 2 sparse bundles of limited max size, one for each computer. Follow the instructions given here
http://fmeus.wordpress.com/2009/04/11/using-drobo-and-drobo-share-with-time-machine/
2 impossible, but you can daisychain drobos together 
For TimeMachine with DroboShare, look for BackMyFruitUp in the DroboApps (Drobo web site). There is a link to download this DroboApp as well as all the needed explanations for the setup (project on Google code).
Cedric