"The home chairs"
Translation:Viti vya nyumbani
They're not the chairs of the house but the chairs of the house-place, ie. the home. Roughly, nyumbani is used when "home" is used in English and nyumba for "house" but it's a bit more nuanced than that.
There are quite a few of these compounds with a locative noun when the second part essentially tells where something is.
taa za barabara
ni = traffic lights (lights of on-the-street)
simu ya mkono
ni = mobile phone (phone of in-the-hand)