My maths are next:
Investor 1: 5 x1
Investor 2: 1 x2
Investor 3: 1 x3
Bankroll = 5*1+1*2+1*3 = 10
Bankroll's shares: investor 1 - 50%, investor 2 - 20%, investor 3 - 30%.
Casino'a wins/losses divides among investors according to their shares.
Dividing the wins/losses among investors changes that 50/20/30 split. You have to recalculate the percentage after every bet.
With the current system that isn't necessary. If you have 10% of the bankroll before a bet, you still have 10% of the bankroll after the bet. The only time your percentage share changes is when people invest or divest.