Je ("them") is the accusative plural case form of oni/ony/ona ("they"). It is the direct object of the verb in this sentence. You might want to have a look at the following site, which is packed with useful information: https://en.wikipedia.org/wiki/Czech_declension#Personal_pronouns.
Do you really have to spell it? In my browser (chrome) and my phone app (android) I don't have to spell "š" and just write Frantisek and the system is ok with it. Goes the same for other letters and for other languages (like o/ö in German). I never had an answer rejected for these reasons, so it's interesting you say they insist.
EDIT: I realized that my experience with Android has to be from other languages, since Czech is not on mobile yet...