Thank you! If I understand correctly, there might be an issue because they come to the US and they are working for (and receiving a salary from) a US company -

Thank you! If I understand correctly, there might be an issue because they come to the US and they are working for (and receiving a salary from) a US company -- no matter if the money are paid abroad. Which violates the ESTA condition. Is that what you meant? To the contrary, if they were working for a EU company (sister of the US company), then they could come to the US under ESTA/working, correct?