When attached to adjectives or nouns, the past suffix has the form -(y)DI. This is due to the older form of the word being idi, which changed over time. :)
No English speaker would use the phrase "its car" unless it were owned by a robot.
Duo interchanges his/her/it to incorporate the notion that onun is able to be used for any three scenarios, in other examples the options for he or she will be used as well