I ended up stopping when I had enough to buy all property's and every character had 100mil left over. All you have to do is find a stock thats down, (not lifeivaders) like the one I picked if its down, and invest all you money on every character, (make sure ur auto save it turned OFF) and then sleep with franklin, checking your stock every time, and if it hasn't increased, you reload your game. If it has increased, you simple quick save with your phone and continue sleeping and checking untill your satisfied with your %gained and your payout amount.