Bookkeeping and accountancy rule here. Until money is in the bank, you can't say its yours and you have to budget on the fact that its a liability.
This means when you plan your budget for a wedding then the entire cost of the wedding is YOUR liability. It is not your guests. Your empty rooms are an asset you can sell, but if you don't then they are an asset you have to write off anyway, by their nature.
Therefore your wedding costs are everyone's room. Its just you may be able to resell that part of your wedding.
Fastday seeing as I'm not actually paying for the rooms, the guests are paying the hotel directly, that's not technically true.
They are paying for a room the same as they would be any hotel they chose.
The only difference is that any unfilled rooms get charged back to me.
^^This is categorically incorrect, and believing that is why you are in the current mess you are in, because you don't properly understand budgeting and didn't properly think about the needs, expectations and budget of your guest you would be selling rooms to. You needed to think about it, in those terms, in the same way any hotel or guest house would need to think about filling rooms to cover their costs.
You are now selling your assets using emotional blackmail if you force guests to move hotels though.
I don't think that's cool, and you use up the asset of goodwill and friendship in doing so too.