Translation:If the house were not big, they would not stay
The tense of the latter part of this sentence is wrong. The translation should be: "if the house were not to be big (if the house isn't big) they wouldn't stay.
I'm not a native English speaker, but isn't it wrong to use "were" about a singular house? isn't it called "was" ? (january 2019)
Were is correct, as ben138225 wrote, when you use the subjunctive mood. In English this is commonly used when you are dealing with conditionals. The clue word is "if". A common example: "If I were you, I wouldn't have done that."
I think these exercises would work much better if we were given the English and had to translate that into Kiswahili. I know that it also needs to be done the other way, but I find it difficult when "If the house were to be not big", "If the house were not to be big" and "Were the house not to be big" are not all acceptable. The concentration on getting a single (often unnatural) format of English is slowing down my learning of Kiswahili!!!!
I already used one hour trying to get the answers "right" for the last lesson, and now I get this again. I'll be back in September...
Awkwardly phrased. Could we assume "to be" is understood and, therefore, unnecessary?