If I understand correctly, 'discipulas' are female students (first declension plural accusative). If so, would 'discipulos' (decond declension plural accudative) be male students? And what would a mixed (male and female) group of students be?
Yes, discipulas is the accusative plural of discipula (nom. plur: discipulae). Discipulos is the accusative plural of discipulus (nom. plur: discipuli).
Generally speaking, masculine plural forms are used for a group containing one or more males (or masculine objects).
Since romance languages generally skip over females [like French does] it would probably just be "discipulos" but if whoever is speaking has the time for it, like our Latin teachers did at school, it would be: "Salvete discipuli discipulaeque!". "-que" is a suffixed particle when you list stuff and is just translated as "and". There is no genus for a mix of both so you have to take your time and say "[male] students and [female] students.".
In the absolute, one could have considered a neutralisation form with "discipulum" and so "discipula" in the plural accusative. But no...
Of course, if you think about it, the neuter gender implies not having any gender as opposed to having both (hence it's from Latin neutrum, meaning neither).
Females are not "skipped" over, there is a neutral in French, but everybody forgot that the neutral does exist. It almost disappeared, but it remained in some structures.