I'm presuming you would actually want a yes or no from #1 before asking #2 so you give yourself the best chance to get the player you wanted. If player #2 responded even just minutes before player #1, say by voice mail, would you stick to your plan even though no one would be wise to it? Say that played out and one of those players then respectfully turned down someone else thinking all was in order only to find out someone had been double dipping so to speak. Maybe I've misinterpreted your suggestion. I'm not sure it would get the best result
The number 1 choice needs to know that she's the first to be asked, but the player also needs to know that the spot in contingent on her saying yes. If her response is "I'll get back to ya..." then she needs to know that there is a chance that it might not be there when she gets back. It's not double dipping. Like an earlier post said, parents should do there homework before the tryouts and should have a plan in case they do get asked. Is it double dipping if the girl goes to another tryout the next day, gets turned down, and then tries to accept with team #1 without accepting any risk? I would reward the girl who is most eager to be with your organization.