Question words at the end or beginning? (e.g. "Nide baba shi shei?")
Chinese is one of the group languages in which question words remain exactly in place of the "questioned" word they replace.

那个人是谁 - 那个人是我妈妈


In English and some other European languages question words always move to the head of the utterance.

Who is this person? This person is my mother.


I highly suspect your examples from Memrise (or whatever that app is) are simply a result of an English speaker (not very fluent in Chinese) translating them to Chinese.

One other explanation:

谁是你爸爸 ~ “which one is your dad"


while 

你爸爸是谁 ~ “and who [exactly] is your dad?"


So, at the beginner level, stick to placing question words in the same position the answer would occupy.