You should honestly ck. with an atty., but when someone/anyone has POA over another person, the one with the POA has the last say over what this person can or cannot do. That's the purpose of a POA. When someone can no longer be capable of making decisions, a POA is drawn up for that person to have COMPLETE control FOR the incapable person who is unable to do for themselves any longer. She CAN keep the son away from him & taking him anywhere, taking advantage of him. She holds the "key" to what he does or doesn't do, she does the thinking & everything else for him. That's her rights as holder of his POA....best to you...:)
If by "trading" you mean stock trading, you don't need to worry about much about law until you start getting into serious complex trades. Just about anything you might need to think about will be handled by your broker. Otherwise, if you need to know the law, go to law school or hire someone to work for you or advise you who did.
Commercial law is very, very broad since it encompasses pretty much any area of law a business will get involved in, from administrative law to toxic torts. Securities law will vary from country to country, since each nation regulates securities differently. Even in the US, there are differences in regulation between state law, Federal law, and exchange rules. Beyond securities, there's contracts, sales, secured lending, lessor/lessee, property, intellectual property, anti-trust, environmental law, employment law, torts, and international law. Each of these areas is distinct and highly technical. Most lawyers that work with high-wealth individuals or large businesses devote most of their adult lives to learning and practicing one single area, though it is possible, with intense study, to learn their fundamentals yourself. Each will require a separate book and immense amounts of time to read, do case studies, and just generally digest the information. If you're really dedicated to that, I'd suggest West's "Nutshell" series and the "Examples and Explanations" series to learn and work with examples of the various points of law each topic will present. Expect to spend around $120 total per subject for those two books.