My model would work best because you wouldn't need to play every week. Only when you feel like it but the winnings would be divided up by all the people named on the submitted scratch cards for that week. No chasing payments, no complications.
If the winnings are low then more scratch cards can be purchased and submitted for the following week. You could set a threshold, if the winnings are less then £50, then use them to buy more scratch cards for the next week.