I adapted this method from here.
It works perfectly to just combine the maps. But now i need individual contol over the strength each of them.
Is there a way to do this ?
If you want to adjust each map individually instead of against each other like in the other answer you need to default to straight normal that is (0.5, 0.5, 1). That means with values you need to find difference to 0.5 and multiply it with your weight before adding it back to the 0.5 for each R and G channel.
(the weight field of normal map is placed under the respectful image node)
Another option is to mix the colors, again mixing both with the straight normal color (0.5, 0.5, 1) individually with adjustable factors.
Both methods should do the trick but in the color example the input values' magnitude is halved because of the way the colors are combined.
I' not sure this solves your problem, but do you see that in the Normal Map node on the right of the image there's the strength bar? I would try to use two of them, one for each normal map and then do the whole setup to combine them.
See the image below for reference. Keep in mind that this setup I made is not the correct one, I just made it really quickly as an example of what I was thinking about, you probably need to "combine" it with your solution, just apply a Normal Map node for each normal map you want to control the strength of.