They manage these huge funds. The people who invested in their funds own the stocks in the funds. Though these companies do vote during stockholder meetings on behalf of their clients without the clients inputs. Thus they wield a lot of power over many companies but they don't own it all. If all their clients decide to drop them and liquidate they lose all that power.

Isn't Vanguard 401ks? Or is that a different Vanguard?

The 3 of them own almost everything

Do they though? They do own a lot but sovereign wealth funds do too plus, unlike those AFAICT, one can easily switch from say a Vanguard ETF to whatever other investment vehicle they want in an instant. So yes they have tremendous power, too much, and they contribute to shaping markets worldwide... but it's also not their actual money and other economical actors do exist.

So I'd argue "own" and "almost everything" is a big exaggerated.

PS: I'm not an economist so that's just my candid understanding.

Is it bad I constantly confuse it for blackwater instead? I guess they murder the previous tenants, then buy up the house?