Using the information from the links you provided and the information found at the Planter's Nuts website (your mileage will vary depending on brand...) and little math (for the peanut's sodium per 100g) we learn that per 100g of each ingredient the sodium content is:
- Nutralite: 786mg/100g
- Amul: 836mg/100g
- Salted Peanuts: 430mg/100g
If the recipe calls for (using the Amul):
- 4 cups of salted peanuts(@150g/cup => 600g peanuts => 2500mg sodium)
- 2 tablespoons of butter (@14g/tablespoon => 28g butter => 234mg
So, loosing 2500mg sodium from the peanuts and only recouping 234mg sodium we need to add 2266 mg of sodium...now, sodium is only about 40% of salt...meaning that we need 5.6 grams of salt...at 6.375g/teaspoon means we should add about a teaspoon of salt.
Mathematically, this 'makes sense', however given that the peanuts are probably to be added at the end I would suggest salting the peanuts directly and then mixing the peanuts(with the salt added) as directed. The process of creaming the butter may distribute the salt a little differently in the mix. I would suggest starting with 3/4 teaspoon of salt then adjusting taste.