By Koh Gui Qing and Milana Vinn

NEW YORK (Reuters) -A bitcoin company tied to President Donald Trump's two oldest sons more than doubled in value in its stock market debut on Wednesday, valuing the sons' stake at well over $1.5 billion as the first family grows their crypto business interests.

Shares in American Bitcoin Corp, a bitcoin miner, soared as high as $14.52 in its first day of trade on the Nasdaq, before pulling back to be up 16.5% at $8.04 by the end of the day.

The company is around 20% owned by Eric Trump and Donald Trump Jr, American Bitcoin Executive Chairman Asher Genoot said in a previous interview.

This values their stake in American Bitcoin at $1.5 billion at the close of trade, based on 908.6 million outstanding shares that American Bitcoin said it had in a September 2 stock exchange filing. The highest price struck by the stock on Wednesday valued their stake at $2.6 billion.

Crypto ventures have become an important driver of growth and potential windfall profits for the president's family, where the family business - The Trump Organization - had in the past focused on building and running real estate projects and golf courses.

"Crypto is exploding," Eric Trump said in an interview on Wednesday. "I would be saying right now, the crypto space is at least 50% of what I'm doing."

The Trump family's forays into crypto have drawn criticisms from Democratic lawmakers and government ethics watchdogs about conflicts of interests. Critics say the Trump family is profiting from crypto at the same time when the president is easing regulations and enforcement on the industry.

Eric Trump, the second son of Trump, dismissed such criticisms on Wednesday as "insane."

"My father has absolutely nothing to do with this venture," Eric Trump said. "He's is running a nation. He's not involved in our businesses in any way, shape or form."

Eric Trump, who holds the titles of co-founder and chief strategy officer at American Bitcoin, described his role at the company as akin to a spokesperson.

"Crypto had a very bad voice for a long time. They really had a hard time communicating a message," Eric Trump said. "I think I've become one of the great spokespeople for crypto over the last, call it, you know, 12 to 18 months," he said. 

"I think I've been able to put a great voice on that, not just here in the U.S., but worldwide."

President Donald Trump has promised to be the "crypto president," saying he backs the asset class because it can improve the banking system and increase the dominance of the U.S. dollar.      

In line with his family's growing crypto interests, Eric Trump has travelled internationally this year to cities including Dubai, Hong Kong and Tokyo to rally foreign support for the crypto industry.

The Trump family has launched a string of crypto ventures in the past year, from American Bitcoin to World Liberty Financial, and meme coins launched by Trump and his wife before the president's inauguration in January. 

World Liberty Financial, which debuted digital tokens known as $WLFI on Monday, has earned the first family around $500 million since its launch last year, according to Reuters' calculations.         

Trump Media & Technology Group and Crypto.com agreed last month to a deal with a blank-check acquisition company to launch a new venture that will pursue a treasury-style strategy to buy the digital token CRO.

Hut 8 Corp, an energy infrastructure company that is also involved in bitcoin mining, owns about 80% of American Bitcoin.

American Bitcoin said in a stock exchange filing on Wednesday it is also selling $2.1 billion worth of shares, and plans to use the proceeds to buy bitcoins or bitcoin mining machines.

(Reporting by Milana Vinn and Koh Gui Qing; additional reporting by Summer Zhen in Hong Kong; Editing by Lincoln Feast.)