The best outcome that can happen to you if you find yourself in such a situation is that you relinquish the domain name for free and nothing further comes from it.
And that costs money.
They've had the domain for years.
Happens all the time, as many brand names come from family names and the founder isn't the only person bearing that name.
What is this based on? Because surely I have the right to own mylastname.suffix without being a business even if someone decides to make a business that bears my family name.
There was famously an apple store employee called "Sam Sung" - https://www.cultofmac.com/290116/sam-sung-auctioning-apple-s...
[1] Hebrew/Israeli name usually transliterated as "Nisan"
Surely they can afford it.
Source: Went to law school. Never practiced though.
Yes, they were here first.