Can I use a narrowide chainring on a double rings crankset? I would like to go touring using my narrowide chainring, but I would like as well to put a smaller chainring (the infamous Grannie) so that I could have it as a last resort in case of really hard climbs (considering that I will carry a lot of gear while touring for several months).

Do you think I will be able to shift gears on the crankset with a front derailler, considering the narrowide chainring?
There would be a 50% chance for a narrow chain link to sit onto a wide tooth during a transition from the small ring to the big ring. This would result in chain misplacement and imminent failure under load [thanks to @mattnz for figuring that out].

Narrow-wide is all about chain retention, while what one needs in a front double by definition is chain derailing easily and reliably.

My suggestion is to have a proper double chainrings. Given that you'll be touring, you'll need to consider possibility of repairs, and finding a new regular chainring would be much easier than a fancy narrow-wide one.

You can also have two front chainrings but no front derailleur. In this case, gear switching happens by hand: stop, throw the chain from one ring to another, and move on. Provided that you do not plan to use the granny gear often, it may turn out to be a viable option.