descendre: why is is descendaient for one example and descendraient for the other? Both are "they got off"

Hi Maeve, 

I have checked and I can't find descendraient ( conditional of descendre) in the lesson,  I can, however, find a past historic or passé simple in French.

Take a look at the following lesson on how the past historic is used -

Passé simple

and how to conjugate verbs like descendre -

https://french.kwiziq.com/revision/grammar/conjugate-regular-dre-verbs-in-le-passe-simple

Bonne Continuation!