Difference between za and ya anyone?
Is kaka a variation of ndugu?
Yes, Ndugu is a synonym for kaka. They both mean brother.
is this phrase used regularly by natives?
Why not "habari za nyumba kaka"? Is ni added whenever you refer to something as a place?
In the specific case of nyumba/nyumbani, the former means "house" and the "latter" means home, most of the time.