Do pilots get full credit hours when they fly double or augmented? In commercial airlines, in some very long flights as far as I know they require double cockpit crew sets (2 pilots, 2 co-pilots) to operate. 

Do both crew sets get the full credit hours for these flights? Or do they get 50% only as they only operate half of the flight? 

It would be nice if there's some sort of airline policy to back up the answer.
It really depends on the individual Air Regulations of each country, and the union contracts of each airline. Pilot union contracts are often more restrictive than the Air Regs of the country they operate in. 

In my experience, North American airlines with "formula pay", both sets of pilots log the entire flight, because they are paid for the entire flight, even when they are sleeping in the bunk. 

Other airlines who pay monthly salaries, with bonuses for extra overtime hours, do not credit the pilot for time in the bunk, and they tend not to log those hours either.