Travel through Namibia Botswana Zambia

Hello, I'm Cristiano!

I'm planning a journey through Namibia Botswana and Zambia with a small group of friends (2-4 people), and i'm not sure about how to do it.
We'd like to rent a car in windhoek and to use it from there to Lusaka but I think that it would be very expensive because it's impossible to return the car in the same office.
Otherwise we could rent a car and return it in windhoek, then move to Botswana and to Zambia with the bus and there rent a different car and do the same way.

Every suggestion is welcome!
also about the period (we were thinking august) and the lenght (20-30 days).
Thank you!!!

Where do you want to go in Zambia and Botswana?

Unlike Namibia, the roads are not that good, and I doubt you can just hire a car and drive off into the sunset.

It may be simpler arranging a small tour with a driver.

Even so, 20 days is not enough for Namibia, never mind 2 other vast countries.

So - purpose of visit? Where do you want to go?

Then we can advise.. :-)