Is it legal if I'm managing my family's entire wealth?
There are two issues. The first is that you can manage all of your family's money. The second issue arises if you now "own" all of your family's money. As far as entities go, it is best to keep money or assets in as many different hands as possible. Right now, if someone sued you and won, they could take away not only your money, but your parents' and brother's money, under your name. Also, there are gift, estate and inheritance tax consequences to your parents and brother handing all their money to you. You should have three or four separate "piles" of money, one for yourself, one for your brother and one for each of your parents, or at least both of them as a couple. If someone sued one parent, the other parent, your brother and you are protected. You can have all these piles of money under your management. That is, your parents and brother should each maintain separate brokerage accounts from yours, and then give you the authorization to trade (but not withdraw from) their accounts. This could all be at the same brokerage house, to make the reporting and other logistics relatively easy.