The company would let customers trade US stocks at very low commission fees.
If you are looking to open a brokerage follow basically what eToro does:
https://www.etoro.com/en-us/customer-service/help/1753170272...
https://www.etoro.com/customer-service/regulation-license/
Seems like getting a Cyprus license for EU clients is the best move. You're in luck as there's a lot less red tape than if you were serving US-based customers.
As far as managing the US assets:
https://www.apexclearing.com/home-2/ https://apexfintechsolutions.com
If you or your partners are serious about entering this business, contact me and I can get you in touch with people who have the experience and connections to get fintechs off the ground: https://femku.com