You can execute POA in favour of your close family member 

POA should be attested before Indian consulate 

similarly your wife can execute specific POA in favour of her close family relative for sale of property 

You should do all these transactions through a power of attorney. Give the Power of attorney to a trustworthy person and he will do transactions on your behalf in India.

Even though you have divorced your wife, since the property is jointly owned, your wife has equal share in the property, hence for selling the property you both have to execute the sale deed jointly in favor of the prospective purchaser. If you both cannot come to India for selling the property and executing the sale deed in person, you both may give power of attorney deed in favor of some close relatives each who will carry out the tasks on your behalf on the basis of the POA deeds executed by you both at Australia and after attestation by a local notary public or attestation by an official of Indian consulate, the power agent can get them adjudicated before the concerned registrar to carry out the assigned tasks on your behalves. . 

1. Both you and your ex-wife authorise someone, preferably a blood relative, to act on your behalf, by executing a POA ( It can be GPA or Special POA) in the name of the Attorney.

2.  By following the above procedure, both of you can sell the property, while you are in Australia.

3.   Similar case I have done successfully for my client, who is an Australian Citizen.

You both have to execute a special PoA in favour of your relative or friend in India for the purpose of selling the property. The Special PoA needs to be either notarized or attested by the Indian High Commission in Australia. Within three months of its arrival in India it has to be adjudicated (assessed for applicable stamp duty in India) by the land registry under whose jurisdiction the property falls. Once done, the power agent can sell and register the property in favour of the buyer.

Dear client,  you  and your wife may appoint general power of attorney for this purposes if you both doesn't want to visit India. 

You can sell the same through poa if you can't come physically. Only the applied tds and taxes will be applicable during receipt of sale consideration

- Since that property is in joint name of you and ex-wifes name then you can jointly sell the same legally to any Indian resident . 

- If you both are unable to come to India , then you can give POA to any relative or nearest person for transferring the said  property to the buyer.

-  POA should be notarized as per rule of Australia and attested from the consulate of India.