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yes, non-resident are required to file tax return and will likely have tax obligations. The form 1040NR is used - http://www.irs.gov/pub/irs-pdf/f1040nr.pdf
each person would need to apply for ITIN - http://www.irs.gov/pub/irs-pdf/fw7.pdf
General withholding rate for non-residents is 30% unless another rate is set by tax treaty.