No. You'll notice there's no m- or wa- on it. It's N- class.
Generally, all animate nouns take the agreement markers of m-wa nouns.
daktari wangu = my doctor
madaktari wangu = my doctors
kiongozi wa chama = party leader
viongozi wa vyama = party leaders
There is an exception for animate N- class nouns, which generally take the y- and z- markers of their group. Otherwise there'd more often be no way to yell plural or singular.
dada yangu = my sister
dada zangu = my sisters
No. I think that "zangu" is correct. But I dont understand why they use "wale". Thats the plural for a M-/Wa- class. Wharever it is, there is a misconcordation from the demonstrative to the posesive.
Yes, as AGreatUserName explained above: The N-class takes the y-/z-connectors; except the demonstratives and verbs still go by class 1/2 as they are animated.
I have seen dada treated as N class (along with baba, mama and kaka) in a few online courses and in Teach Yourself Swahili by Joan Russell, but my tutor corrected me with "madada", and he is a Tanzanian linguist. He is also in the majority when I searched among online sources, so I wonder if this depends on the variant of Swahili.
Since dada langu/yangu can be elided to dadangu, I can see how people might start arguing about which class it is.
After further discussion with my class tutor, it looks like some Swahili speakers add "ma-" on to "dada" because they are unsure about the noun class and instinctively want to see a plural marker. (In the same way, English children and ESL students may say "sheeps" as the plural of "sheep" because it doesn't sound right that both the singular and the plural are the same: "There are three sheep in the field.")
Both "dada zangu" and "madada yangu" are accepted as the plural. (As Gazelle1596 points out, you can find both in the dictionary.) I think "dada zangu" is considered more correct though.
You will also see "rafiki zangu" and "marafiki yangu" both used to mean "my friends".
Note that other kinship nouns that come from Arabic are also in the N (9/10) class: baba (father), mama (mother), kaka (brother), bibi (grandmother), babu (grandfather), shangazi (aunt), binamu (cousin).
So sorry but " dada" belongs to cl. 5/6 JI-MA because it is arabic kind of noun. As a human is treated by 1/2 M-WA class this is why it is " wale" (plural) but....then it should to be - yangu ( plural 5/6 JI- MA )
dada noun 5/6, animate sister