1)both Swathi and Nagesh have to give POA to Ramesh to sell the property .
2) the POA has to be registered .
3) if POA is only for booking apartment and doing bank work Ramesh cannot sell property standing in name of his ister and brother in law
4) consult a local lawyer before taking any decision
5) go in for bank loan for purchase of property . bank will do due diligence before sanction of loan