If both taxpayers have ITINs, they will not receive anything on the first payment (nor will they be eligible for anything).

My understanding of the 2nd payment is that if they have eligible children (i.e. child with a valid SSN under age 17 who lived with them in the US -- NOT IN MEXICO) they will get the $600 for the child, but not for themselves.

Anything regarding the 3rd payment is pure speculation, as it isn't even being discussed in congress yet, let alone written and voted on. 

I've just looked, and the worksheet does NOT calculate this correctly. If you enter an ITIN, it still calculates as if they get the payment. So you must over-ride the entry and show that they should NOT get this as a refundable credit.