The three partners agree that they must know whether it was one of them who made the girl pregnant (thus possibly allowing a suit against the company) or if it was someone else.
How can they decide if one of them is to blame, without anybody having to accept being the father, if that was the case?
(Some notes: They might just write on papers either "I DID IT" or "I WASN'T IT", but the handwriting might give the guilty party away. Putting a white or black marble in an urn (white=innocent, black=guilty) might work, but someone could possibly see what color was being put in; also, if the guilty one went first, the second could peek inside and realize the answer. The optimum solution should not require much --or any-- extra equipment, and should "resist" inquisitive partners. And, of course, being all of them quite capable hackers, computers are out of the question!)