What i see here are a group of rays that have been sitting in a holding station in Brasil in poor conditions for many weeks even months without proper care and certainly little or "no" food.Then they have been shipped in this emmaciated state which to me is horrifying!! To make things worse they have then been quickly moved on to you from the supplier. All new imports need a few weeks to settle and become established in captivity before been sold. I don't know the guy you bought them off, he is probably a very nice fella but I have to say he's slipped up moving such fish like that onto a customer!
Unfair to the rays and unfair to you!
Such fish require close observation,many will feed which is always a good start for any ray keeper but there is every chance such weak specimens could be suffering with internal parasites, this will soon be evident if they fail to gain weight, think some Prazi will be needed at some stage.
I hope you don't experience any problems along the way...I really do.
Best of look with them!