And I would be extremely wary of your plan to do this with friends, because what happens in the 'worst case senario' and someone looses a job, or otherwise can no longer afford to service their portion of the loan. Unfortunately the banks will not care that you have already paid you portion, they will expect you to cover the rest as well. You will be liable for the entire debt, if for some reason they decide not to pay.
I would've thought that we would each have our own seperate mortgage and finance. Is that not possible?

Yes if they had to get out in the middle of it all we'd probably be forced to sell up too because we wouldn't be in the position to buy them out, but with the financial side of things being handled separately at least our credit and assetts would still be in tact.