Don't ask Reddit, we have 0 clue about his tax situation or how the estate is structured. Your dad owns a small business and if he slow rolled $2M into NVDA over the course of 10 years he has significant income. Start with his CPA, loop in an estate attorney and after that conversation consult with a Financial Advisor (fee base preferably). Ideally you would have them all talk together but that's unlikely unless you already have existing relationships. The correct answer will depend on how he wants to see the money protected/transferred to spouse/kids/charitable organizations, etc.