power of attorney

Any document by which you propose or are desirous of gettig a transaction done  in respect of an  immovable property needs to be done by a registered document, including this power of attorney deed.

There is no exception for  family relationship in this regard

No, it cannot be done online, the POA executor if residing in a foreign country can get it prepared in that country, duly attrested by a local notary public or by an official of Indian embassy and send it by a sealed cover to the chosen power agent back in India, who will then get it adjudicated by the concerned sub registrar, subsequent to which the power agent would be able to perform the tasks assigned in the power deed.