I would think that the due diligence would be carried out by the prospective buyer's accountants and lawyers. If 2 buyers used the same set of accountants and or lawyers then I would guess some saving of time might me made. However, it is highly unlikely that they would use the same, so it would probably take the same time.
I see where you are coming from, John, but it is not where I am suggesting some time can be saved.
For instance, let's say Allam had decided he was going to sell his business and he wished for a swift closure of a deal (sic).
Let us presume that as a highly experienced businessman he broadly knew what questions would come at him in any prospective buyers Due Diligence.
Lets make this a tad simpler than it often is, but lets assume he would expect questions on two general fronts: Accounts and Assets (they will eventually merge, we know that.).
He will make sure his accountants are prepared to issue the answers to questions on P&L, etc.
But he also knows that he has properties and that those properties house quite a bit of equipment (assets) and he knows it is usual for an audit of those assets to be required.
To audit those assets would mean a team from each seperate buyer tying up his staff for some considerable period, this multiplied by the number of prospective buyers. Anyone who has experienced this would know that if the company has not kept robust records (many do not) this can be very detrimental to day-to-day business.
Or he could appoint a fully accredited, independent auditor (for arguments sake, Price Waterhouse Cooper - they might tackle this type of thing, it's a random guess) and offer that to each buyer as the basis for their assements. I think most clued up businesses would accept that, simply questioning any elements they are unclear about. It is this that can make any subsequent Due Diligence shorter in duration,
if the independent audit was triggered by the first enquiry and not pre-prepared (as they have a time limitation).
I have never come across two buyers sharing accountants and/or solicitors and I believe there would be a conflict of interest in doing so.