Murtaza Bhaee, I have a few suggestions.
18th night, they can opt for Eagles nest. Hotel itself is okay but scenery and atmosphere is awesome.
19th night, Question, why would they travel from Hunza to Isb and then on 20th take fly from isb to skardu?
Maybe they could do this:
19th , hire 4x4 and go from hunza to astore. Stay in Astore and maybe take a quick peak at Rama meadows.
20th, astore to skardu, stay in Shangrila skardu. They can visit deosai along the way etc.
21st, stay in Shangrila skardu, visit kachura lakes and relax in serene atmosphere.
Still with all this, I consider @nagar1 bhaee an authority. Lol