Most cream leather would be pigment coated rather than aniline style but the absorbency rate of your cleaning products will tell you how much pigment coating there is so they may be micropigment. The Five step process will tell you all the info you need before you start. However on closer inspection the backs do appear to be made of something different, possibly microfibre, again a microscope will help here.
The degree to which any grease has been absorbed and of course doing the leather ID process would be crucial before starting any job.
The surface of the leather could quite easily be greasy in this environment, have seen it before in restaurant situations. However if the owner has noticed that they are greasy this may also indicate that the are not actually leather at all which has been suggested.
Hope this helps
Judyb