On mobile not all words seem to have audio. Is this different on the desktop version?
Duolingo uses 3rd party commercial text to speech engines to read the exercises in most of the other languages. There are no 3rd party commercial text to speech engines available for Irish, so, instead of leaving the Irish course with no audio at all, Duolingo arranged for over 4,000 exercises to be recorded, and manually attached these recordings to the relevant exercises.
The website and the various different mobile app versions of Duolingo all use the same set of exercises and audio files.
The Latin translation would be Viri legunt, so the relation to Léann na fir can certainly be seen.
It's not in the genitive, "fir" is the plural of "fear".
In some cases, such as "fear", the plural and the genitive take the same form, but in this case, it's clearly not a genitive construction, it's a plural nominative construction.
Can it also be translated as "the men are reading", or the continuous form is expressed differently?
You can log into the website on your phone to access the Tips & Notes. That way, you can switch over and read them even when you are in the middle of an exercise.
The progressive form is expressed differently. To native speakers, this is a habitual action.