I only read half of this but it sound very much like this manga a read not to long ago. 

I think it might have been an Yaoi (Or it was a little fan serves put in) 
It was about two twins humans. They got sent to another world turning them into nekos. However you find out that the twins were just one powerful neko who master sent him to the human world splitting his soul into half. 

It had all that jewel as kind of heart things. God I wish I remembered the name of the manga it was pretty good and still on going. 

Anyways I will read the rest later to see if I want to join or not.