Luigi
Not sure you've quite got it, yet.
Saab, I'll take into consideration that passengers can only pay towards the cost of flying, eg, 2/3 in total, that is fine, as I'm happy to pay 1/3 of what I normally pay.
If you have 1 pax you must pay at least half, 2 pax means a third and 3 pax a quarter.
Just wanted to make sure it was clear.
I don't even know what a facebook is.