Thanks for the recommendations.
Would it be better to do Waterberg Plateau for 2 nights and then head to WDH for a afternoon flight or do Damaraland for 1 night and then Okonjima for the 2nd night? We could do Waterberg Plateau on the 2nd night but from what I see, it is about a 3.5hr drive from Damaraland to Waterberg Plateau (and Okonjima seems to be somewhere in between Damaraland and Waterberg Plateau). With the family, I know there won't be much hiking and that's why I kinda excluded Sossusvlei from the start and I'm not sure of the other sites.
I guess it also depends on how many days we spend in Etosha. 10th is a lost day (flying in plus driving). 11,12, and 13th are full days for Etosha. 14th and 15th are the "free days". We could also do Okonjima on the 14th, heading then to Waterberg Plateau for the evening and then Waterberg Plateau all day on the 15th.

I guess the choices are:
1. 14th and 15th in Waterberg Plateau
2. 14th Okonjima and then drive to Waterberg Plateau in the evening. Overnight Waterberg Plateau 14th and 15th (site-seeing Waterberg Plateau on the 15th).
3. 14th Damaraland and 15th Okonjima
4. 14th Damaraland and 15th Waterberg Plateau