According the Tailless Cat Rescue and a breeder they consulted, the rescued cats are not Manx cats - they are Japanese Bobtails. You don't see Japanese Bobtails often in rescue because it's a recessive gene - but there were so many generations of cats in that house, it's no wonder there are so many Japanese Bobtails there.
This is what I learned today about Manx versus Japanese Bobtail...the bone in the bobtail of a Manx cat is always straight. Manx tend to be shorter legged and very round, like basketballs with legs. The bones in bobtails on Japanese Bobtails are always curved, hooked, or twisted. JB's are leaner looking cats, longer legged, with large ears and angular faces. And apparently solid black Japanese Bobtails are rare.
Who knew? Certainly not me! I know "alley cats". And to me it doesn't matter if they are a rare cat or an average run of the mill cat, we're glad we could help them. I hope to get more pictures of them up soon.
I just went in and spent some time with them before maybe trying to get to bed at a decent time tonight (decent time means before 3 AM!). The younger one is still skittish, but let me pick her up with only a tiny bit of hesitation and started purring immediately. YAY!