Income tax benefit for hra and home loan

Hi,

   I want to know the rules of claiming HRA and Home loan benefit claim in the following situation,

1. It is said that the both the benefits can be claimed if the rented property and the property (against which the home loan is taken), if they are not the same city. What is the city boundary to be considered for this rule? I stay in Kolkata, and both the property (Rented and the property) are with Kolkata pin codes and under Kolkata Municipal corporation (but different pin codes, different Thana and different constituency, zilla is south 24 parganas, not kolkata). 

2. But I know ta deductions still can be claimed (with proper justification) if I am not elligible by the above mentioned rule. I stay with my mother (the rented place) and I need to stay with her to look after as she is old and not well (also she does not have any other income source so the rent is required for her living). Can I claim the tax benefit on the basis of the above grounds? My mother has the pan number and tax return is filled every year with the rent amount mentioned as income. 

Thanks in advance for the reply.