Sorry to hear about what happened to the families, no doubt the estate agents will escape any punishment and get away with your money, (can you not go to bank and cancel the pre signed cheques?)
and of course the local Qatari owner will not lose any sleep over sleep over this and will attend his prayers as a good and humane muslim no doubt. I assume that the Police acted legally in that there was probably some order issued to the agents who ignored it as long as they could cash the cheques!

In addition to the newspapers, why not go to the TV News station? I am sure that they would be interested. I have had dealings with some of the embassies here and they are pretty toothless so dont hold your breath, as for human rights Qatar are not signatories.

I would also write back to your home newspapers, (also places like UK, USA may also be interested in seeing how Qatar treats its expats!) or get them online, Qatar is all about image, stories such as this tarnish that image abroad and will probably be more effective in getting a response than trying to take locals to court!
I hope you contact sl and take him up on his kind offer of help and advice.