"That is his sister"
Translation:Yule ni dada yake
Where have you seen dada listed as belonging to 5/6?
Kinship names (other than mwana, mume, mke) are generally 9/10 and for the possessives they use the y- and z- forms to indicate plural and singular.
mama yangu = my mother
mama zangu = my mothers
baba yangu = my father
baba zangu = my fathers
kaka yangu = my brother
kaka zangu = my brothers
dada yangu = my sister
dada zangu = my sisters
Same with bibi/nyanya and babu, ndugu, shemeji and a bunch of others.
These words sometimes get a ma- in the plural which seems to be a non-standard thing, such as "rafiki", which is commonly:
rafiki yangu = my friend
marafiki zangu / rafiki zangu = my friends
But that's pretty rare with dada.