Resale flat by 2 ND owner buy flat by irrevocable power of attorney registered by paying stamp duty

I am willing to buy resale flat.the 2nd owner buy flat from 1st owner.the owner give irrevocable power of attorney to 2nd owner and 2nd owner done registration in register office by paying stamp duty.1st owner buy flat 1996.2nd owner buy flat 2001 but he register it in 2005 .when we ask 2nd owner he is saying society was not form during 2001 and owner gives irrevocable power of attorney for all other process also owner vacant the place itself in 2001.due to health issue of his wife he could not available for other process .it is not mentioned in irrevocable power of attorney.2nd owner now want to sale flat can it be possible to buy this flat is there any legal issue after buying this flat.the 2nd owner has share certificate transfer on his name,NOC from society to sale flat, property tax receipt on his name, maintenance bill on his name but not light bill still on builder name.so can he sold this property to 3rd owner.my side complete white Money not a single rupee black.bank loan and rest by check.2nd owner saying whatever the agent said we followed the procedure.the agent is reputed as far my concern he has sign on agreement .we will ask about this issue with him. Kindly suggest to deal or not to avoid any legal issue in future.