Taxes for Europeans working for USA llc- short term

The best way would be to contract them or go through an agency like Manpower that actually already have offices in the country where your artists live.

The reasons for that are not just the tax situation but also labor laws:

• In the US for example you cannot legally hire someone who doesn't have a legal immigration status in the United States so before you can hire a foreigner you will need to get an H-1B or H-2B visa for them but since your hire duration is about 1 month you may not get this approved.
• Technically you can establish a subsidiary or a branch of your company in a European nation or nations as the case may be and hire them there. Problem is that you will be subject to taxes in those countries and also subject to labor laws of those countries so your 1 month project may become multi-month(years?) necessity to pay their salaries.

Now if you subcontract you will have no issue with taxes and all you will need to provide them would be a 1099 at the end of the year.

I'm pretty sure the answer is simple: you cannot hire them. If the Europeans don't have a US citizenship/green card, or otherwise eligible to work in the US - you cannot hire them as employees.

You're not required to verify employment eligibility for contractors, but knowingly employing illegal immigrants (i.e.: aliens not eligible for employment) is IMHO a Federal offense. If they're in Europe - then you can definitely contract them.