I have not seen anything in the tax code that says that 4 separate checks are required. However, you may want to prepare a "gift letter" that details the arrangement, and keep a copy with your records.
Also beware, the lender will probably require a gift letter that says that the money is a gift and does not have to be repaid. This is because the lender does not want the borrower to have additional undisclosed or secret loans. If the home purchase has a problem, or if your friends' finances have a problem, or your relationship has a problem, they can use that gift letter to argue that they don't owe you any repayment. It could make suing them very difficult.
