I tried to translate as "we are seeing four people" which was rejected and the correction was "we can see four people", but the can is not necessary in this sentence - the translation here doesn't have it. Is there a reason why present continuous is not suitable here?
Present continuous is not used in English when it comes to senses. We are seeing or hearing gives an impression that you are hallucinating and seeing things. SEE or CAN SEE are used even when the process is currently happening.