My "we are sending his computer" was rejected. Should there be a different word when singular..?
Yes, it needs to be computers in this sentence. "Za" means it's plural, in singular it would be "ya" if I'm not wrong.
That is correct (for the N class). Please be aware that the words are different in each class, and that "ya" is actually for plural in the M/MI and the JI/MA classes.
The sentences are written by Tanzanians so I'm trusting that it can be said that way, even though to my non-native ear the way you give here sounds better. If you think it is wrong, though, did yo use the report function?
What's your previous experience with Swahili? Not second guessing you, genuinely curious.