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Is it legal if I'm managing my family's entire wealth?
If you go through the web pages of some online brokers, you will find out that some of them allow you to manage friends/relatives accounts from your account as a trusteer. That should really solve your underlying problem, you will need only one login, etc. (Example: https://www.interactivebrokers.com/ff/en/main.php) If I understand it right it will even allow you to make one trade splitting the cost and returns among the other accounts, but you would have to verify that. Anyways, that will save you a lot of trouble and your broker can probably help you with the legal necessities.