You're the one who didn't think this through.
Think of it like having 25 tickets to the Super Bowl. Ok, so you know who you want to invite and you offer those 25 people. Everyone who says yes, you say alright they're going. The problem is some of these people refuse to tell you right away, they want to wait until the day of the Super Bowl. You on the other hand refuse to allow these tickets to go to waste. So, you go out and you offer more people, but you start explaining the situation. You have 25 tickets, you've invited other people, but some aren't sure yet if they want to go, so on so forth. Over time more people accept but a few people aren't able to go or change their minds.
In the end, you end up the day of the Super Bowl with a few people still trying to make up their mind. That's the day when, surprise surprise you might have to make up their mind for them. Sorry, they had plenty of time to figure this one out, if there ends up being issues it's created by the indecision of the people being offered tickets. And yes, sometimes there is someone more important to you that you are going to keep a ticket for no matter what...