"They come here no longer" sounds acceptable also?
Hardly. It sounds very off to me.
why does the drop down translation say doesn't ??? and the exercise is about They:::
Nechodí can be both singuular or pluural. He, She, It and They are all possible.
shouldn't it then also say don't?
Don't expect the hints to be complete, they are just hints, not a dictionary.
Besides, it contains both. Duolingo then desides what to display.
i see. Anyway I only saw one.