I really like this solution: https://www.cs.otago.ac.nz/staffpriv/ok/santa/index.htm

The problem as stated seems ill posed to me. If Santa wakes up when either quorum is ready, then it's never true that both are waiting unless they arrive simultaneously. Either that's a zero probability event that can be safely ignored, or it needs to be handled by arbitration in some form. Attempting to resolve contention by giving preference to one or the other shifts the problem to that of determining whether they're close enough to be considered simultaneous, with edge cases needing to be resolved by arbitration, and so on.