You have an auction item where a couple of people, or more, have decided to go in together to purchase the item.  So, the next question is sometimes, can each of us pay a portion?

Option #1.  One of you should pay the full amount and the others pay them back for their share.  Unless there is a tax deductible value on the item, and one is willing, this is the easiest way to solve this situation.

Option #2.  Each person writes a check for their share and you send out receipts later.  (At an event, you want to keep it simple and do the busy work the next day.)

Resolution Option #1.  Clone the auction item so you have 2+ (depending on the number of winners).  Mark them in the Setup and Pricing panel, Venue = Onsite and Sale Type = Bid sheet/live. Always save your changes.  Now, you can go in and create a winner for each item based on the user and the amount they will pay.  

Resolution Option #2.  Change the item to a fixed priced item.  Change the quantity of available inventory to the number of purchasers. Then, go into the Fixed Priced tab and create orders for each of the purchasers.  

NOTE:  Be sure to change the estimated value on the auction or fixed priced item.  It should be divided by the number of buyers.  For example, if there are (2) buyers paying for an item valued at $200 and they are paying a total of $300, you want each of their receipts to show that they paid $150 each for an item that, for their part, is valued at $100 or 1/2.  Then their receipts will show that  a portion, in this case $50, is above the value so it may be tax deductible.

Checkout.  You can ask your participants to pay for their share in their checkout cart as they will have pending orders.  Or, if you have their credit card on file or they pay by check, you can check them out in the Financials > Pending area.