Be extremely careful. Use some of that money to hire a lawyer before you send any money to anyone.
Look up "Advance Fee Scam" on your favorite search engine. There are thousands of examples. Never pay out money to get more money.
The US does not tax large gifts to the recipient. (There is a report that must be filed for gifts from foreign persons of more than $100,000 but there is no tax owed.)
If the Netherlands or England supposedly taxes this gift, that tax should be paid by the giver before the balance is sent to you, not paid by you before you get the money.
Assuming this is a real gift, gifts are gifts, not contracts. Once you get the money you can legally keep it all. If this is a contingent gift (you must do X to get Y) then it is a contract and you should have any contract involving that large an amount of money reviewed by a competent attorney before you agree to anything. Attorneys also have escrow accounts that can hold the "taxes" so they are paid properly, if they are real.
But it's probably a scam.
