I believe it is legal. Here in the US, there is the Investment Advisor Act of 1940. It says that if you are an investment advisor you need to be registered. You are only considered an investment advisor if you charge for your advice. So if you are doing this free, this act does not apply.
In your case, you are charging and therefore you would be considered an investment advisor. However, if you have only a few clients and no place of business you may not have to register. There is a de minimis exception. The details of this exception is very important and you need to understand them to see if they apply to you. However, you still need to follow the rules of the Investment Advisor Act of 1940.
Under the act, if you elect to hold their funds in your name then there are some rules you need to follow. Most investment advisor's do not take custody of client's funds.
Also being an investment advisor has other rules to follow related to records. Do you plan to follow these rules? There are books on the rules. Have you read them? If you are serious about doing this, talking to a lawyer is a good idea.
I have managed money for individuals without being registered. I was not breaking the law. This fact was confirmed by my lawyer and a NJ securities regulator. I did not take possession of client funds. That is, the funds I was managing was held by a broker in the client's name.
There are rules about how you charge your clients. You need to follow them.
If you are going to do this, I would strongly recommend that you talk to a lawyer who has helped people like you in the past.
If you are not registered then you cannot hold yourself out to the general public as an investment advisor and you can have only a few clients. Therefore, being registered has a big advantage.
In support of my argument that you do not have to always be registered, you can look at the following URL:
https://beachstreetlegal.com/state-de-minimis-registration-considerations-for-advisors/
If you look here:
https://www.govinfo.gov/content/pkg/COMPS-1878/pdf/COMPS-1878.pdf
On page 38, it says:
(d) NATIONAL DE MINIMIS STANDARD.—No law of any State or
political subdivision thereof requiring the registration, licensing, or
qualification as an investment adviser shall require an investment
adviser to register with the securities commissioner of the State (or
any agency or officer performing like functions) or to comply with
such law (other than any provision thereof prohibiting fraudulent
conduct) if the investment adviser—
(1) does not have a place of business located within the
State; and
(2) during the preceding 12-month period, has had fewer
than 6 clients who are residents of that State.