Shit happens. Refactoring options and shifting things around may suck, but it may have been a requirement of them getting the seed funding. 100% of your options at Zero worth are worse than N% (not a terrible N%) at an actual positive valuation.

I'm not familiar with EU tax rates on short term capital gains in a US market, and would highly recommend spending some of the money you might have spent on a lawyer talking to a reputable financial accountant from your country with experience in this area. In the US you have to set aside a chunk of the proceeds if you do a same day sale when you exercise your options, and are frequently penalized by your state if you don't give them their share at the end of that financial quarter.

There's a lot going on there and I don't think HN is going to give you complete enough advice to rest your mind.