This is complex! If the $250-300k were services, the gain on the sale might be ordinary income. Of not it would be US based capital gains. Since the offshore company appears to be selling a US asset it would be taxable in the US. Before the transaction takes place, ut may be possible to structure this in a tax-free or tax reduced manner. BUT, this will require a lot of information and planning.
You need a good tax and business attorney before you go any further.
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The best few thousand dollars you will spend would be to hire a experienced business and tax lawyer to consult with.
You should not expect any reliable response from anyone based on your very short and general facts.
Lots of documents, agreement and taxes must be reviewed and the prospective transaction to be dissected to explore all tax and liability issues.
Best of luck.
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