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1) What country or countries are they from?
2) Are they using someone else's SSA numbers, or, are they using fake numbers?
3) Are you still employing them?
4) What are their positions?
5) What are their educational backgrounds?
6) How did they cross into the USA? With a valid visa and then overstay, or, without inspection?
This is not an answer, but an information request. I need this information to answer your question. Please reply, so I can answer your question. Thank you in advance.