Those companies can't manipulate the price because the percentage of their holdings is not enough to do that and it will not be on their best interest to do such price manipulation. BTC price is driven by supply and demand in the market. Now, do you think, if few people can control the market, there will be supply and demand that will happen? I don't think so. So to have a healthy market, they won't hoard massive amount of btc, which will give good market movement.
Even if they claim that they have big funds to buy more bitcoin, they will not have a chance to shake the price. Okay, maybe they can shake the price at a small exchange, but they can not shake at a medium or big exchange because the whales in that exchange will prevent their moves and watch their step. As long as the supply and demand still high in the market, that company can not do anything except following the price, but those companies can buy or sell bitcoin at a level price and make people panic temporarily.