Am I losing the reward of Nafl because of my Qadha Salaah?

(2) Likewise, if i pray my missed make up salat at salatul duha time, then will I get the reward of duha salat as well, since I am praying at that time.

In this type of cases, do I need to make dual intention or what? I feel that I am losing the reward of the Nafl Salaah.

You will not get the reward for the Nafl Salaah while performing the Fardh Qadha. The Fardh stands on its own and does not take a dual intention. Dual/multiple intentions can be made for Nafl, not Fardh.

What you will get is the reward for Fardh which is far, far superior to the reward of Nafl. The performance of the Fardh is the means to your salvation and the key that will open Jannah.

The Nafl is similar to the garnishing of a food and the Fardh is the food itself. The garnishing adds flavour and beauty to the food but if the food is missing, then the garnishing loses its point.

Hence, do not feel that you are losing out by not performing the Nafl. Devote your time to the completion of your Qadha Salaah which is your obligation and which nets the greatest reward. Once the Fardh is taken care of, you may then “garnish” your Fardh with the Nafl.

And Allah Ta’ala Knows Best