TD Ameritrade does state that non US citizens can open trading accounts with them to trade in the US stock market. The specifics of what is allowed, what banks, etc, is what I am concerned with. Non US citizens will be taxed by their own country which is different for each country. I am hoping to find a non us citizen, in this case a Thai citizen, who is already investing in the US stock market so they can inform me so I can inform the people I am trying to help.
The money laundering part, whether I initially finance them or not, as long as I am not receiving large sums of 'untracked' cash from them, (which the legal issue here for the federal government is me and others not letting the federal government take a chunk of that money and using it however they want'), is not money laundering. Basically all I am doing is helping non a US citizen invest in the US stock market. There's nothing illegal about that.
I could just ask TD Ameritrade myself, but I think they won't be able to inform me much in the process unless I'm applying as a non US citizen myself. Prob the best I can get from them is what kind of banks do Thai citizens usually use in which case that might be enough.