You both may have to execute two different power of attorney deeds for both to your respective blood relatives and they both can jointly execute the registered sale deed in favor of the prospective buyer. 

Joint POA deed executed by both in favor of her father may not be accepted by the registrar. 

You need to execute 2 different POA which are in the blood relationship with you and your wife respectively.

1) Your father in law is not your blood relative 

2) execute POA for your share in property in favour of your parents or siblings 

3) it should be attested before Indian consulate 

4) your wife can execute POA in favour of her father 

1. There's no bar for giving POA to a non-blood relative also. However the Stamp Duty charges will be equivalent to the Stamp Duty charges for the actual sale deed. However, if it were to be between blood relatives, the stamp duty will not be high.

2.  Since you will not be considered as blood relative to your father-in-law, you can seperately give POA to your blood relative in respect of your share in the property. Similarly, as you have rightly suggested, let your wife give POA to her father (your father-in-law). Let both the POAs execute the sale deed to the prospective buyer in the jurisdictional Sub Registrar's Office, on behalf of you and your wife.

1. In case of non blood relative, the stamp duty for the GPA will be charged not for the individual share on the property but on joint ownership.

2. Hence it's recommended to give POA to a blood relative so that the Stamp Duty is minimal. For instance in Karnataka, the Stamp Duty for POA amongst blood relatives is less than Rs.500/-.

Stamp duty on POA in Maharashtra is Rs 500 if given in favour of family member 

if given in favour of third party it would be around 5 per cent of market value of property as per circle rate 

it has to be paid as per share of proeprty held by person 

sale deed would reflect share of co owners of property 

if there is nothing specifically stated in your title document for the exact share of the co-owners then it will be presumed that both are equal co-owners i.e. 50-50

you can give a POA to your blood relative and your wife can give to hers, to save the stamp duty payable on the POA if it were to be given to a non-blood relative

a single POA can be made wherein you and your wife would jointly grant power to your respective blood relatives under the same document 

Without documentary evidence how can you prove that you own only that extent of property that you claim to be a owner.

The stamp duty shall be on the power of attorney deed alone and not on the sale consideration amount.

You may first consult an advocate in the local who has good knowledge about the applicable stamp duty on different deeds on different occasions and proceed.

Sir 

I will suggest you to execute two power of attorney to avoid any legal complication. One by you and one by your wife.

The stamp paper required is Rs 50/- for it however on safer side take the stamp paper of Rs 100/-. (nothing else is required)

Now....

1. You can take put the printout of the attorney on plain paper and get it attested in your country. Then send it to attorney and he will attach a paper of Rs 100 and get it notarised. It's ready for use

2. Get 2 Rs 100 papers from india and take printouts of both attorneys and get it attested at your place. Send it to attorney and he will get it attested in india. It is ready to use.

Since power of attorney is not transferring any property to attorney holder so only this much stam duty is payable.

I guess your queries have been resolved as there is no major expenses in giving POA. Give attorney to whomsover you want. It's a cheap process don't worry. Just make sure you give proper attorney or you may be asked to reframe it, which will consume more time and effort. Get the attorney drafted from a lawyer and save hassles. 

1. The stamp duty, if the GPA is in favour of a non-blood relative, will be relatively low.

2. In case of joint GPA, the stamp duty will be proportionate to the share of principal (herein co-owner.).

It would depend upon market value of property 

since your father in law is not your blood relative POA in favour of FIL has to be stamped as conveyance 

- Yes, after executing POA dully notarized as per the rule of that country ,and attested from the consulate of India ,you can authorise any family member or nearest one , to execute a deed in favour of purchaser. 

- That POA is valid in India for transferring the property on your behalf , and its registration is not mandatory. 

- Further , for registration of sale deed , the purchaser will bear the stamp duty . 

- Hence, you can give POA to your parents or siblings , and wife can give authority to her father in India. 

The Adjudication fee for the GPA will be less than Rs. 500/- + incidental charges. The Adjudication has to be done in the jurisdictional District Registrar's Office.

Article 41 of the Karnataka Stamp Act prescribes the stamp duty leviable.

Generally, the stamp duty payable for a power of attorney is Rs 100.

For a general power of attorney given to promoters and developers, the stamp duty applicable is Rs 1000 and registration charges are Rs 100. In case it has been given for consideration , the stamp duty applicable is the same as the stamp duty payable on the sale deed of a property, and is based on the market value of the property.

In case it is in favour of a family member for sale of a property in Karnataka, the stamp duty applicable is Rs 100. If it is in favour of some other person, the stamp duty applicable is as on the sale deed - on the market value of the property plus one percent registration charges.