Hi
The main difference between GPA and SPA is that GPA creates an Agency in the recipient (your father-in-law) for all transactions on behalf of the principal (you and your husband), while the SPA creates a restricted Agency (authority) with respect to only the specified acts. Hence, this is more or less a question of trust and can be better decided by you only.
The POA has to be issued by the actual owner of the property. If you both jointly own it, you can both jointly issue a single POA. Two attesting witnesses would be required for the same, though. It can be issued on a white paper from your end. After receiving the GPA in Andhra Pradesh, your father-in-law shall take the GPA to the concerned District Registrar, and get it stamped under Section 18 of Indian Stamp Act, 1899 with Rs.1000/-, as is the case if it is given to a family member.
You will also have to fill the form u/s 32A of the Registrations Act for fulfilling the purpose.
The Registration Cost is 0.5% of the concerned property with a bracket of Rs. 1000 to Rs. 20,000 as the minimum and maximum value.
The Stamp Duty of Rs. 1000/- is mentioned above already.
Regards