Tax requirements for non-US contractors?

I work with contractors often, and of course go the W-9 + 1099 route with US-based folks. I'll be hiring a handful of part-time non-US contract developers soon (one in Brazil, one in Switzerland). Just curious what, if any, tax filing requirements I need to look into that would correspond to W-9 and 1099?

Can't find the same info for Brazil, but here is the exact same question asked by a contractor in Switzherland, and here is another one.

Based on the best I can figure you issue a 1099 to both and they file with IRS form 1042 and based on the Double Taxation treaties existing between US and Brazil and US and Switzerland they will get credit for any taxes paid in the US.