The cracked skin suggests Magadi I think (or mayb Malindi) - would also make sense as he was in with Asani, and this looks like the paddock that they occupy (the VERY old rhino house, as opposed to the old on-show one that is now off-show - was it a barasinga house originally, or something similar?)
Magadi would never tolerate a young bull like Asani and he is not his son! The only reason I can tell this is Kitani is because of her horn which is very similiar to Ema's apart from Ema's is slightly smaller
Given your track record of IDing animals at Chester,I'm with Nisha that its Ema and Bashira,but I stand to be corrected if i'm wrong!
Fair play - I can't ID the rhinos well other than by paddock, and this to me looks like the old paddock opposite the Tsavo aviary - I know for a fact that Asani was in with either Magadi or Malindi at some point though, just can't remember which.
Given as this photo was taken June 2010,why are we trying to working out which rhino is which as Chester will have changed them round atleast 4 times since this photo was taken!!
I would just like to confirm that this is Asani and Malindi. I worked this out sometime ago but never thought to update this photo