"Your father is talking."
Translation:Μιλά ο πατέρας σου.
Because that makes no sense in Greek -- just like "Your father is talks" would make no sense in English.
Greek doesn't have separate present continuous and present simple tenses -- it just has one present tense.
So μιλάει can be translated either as "is talking" or as "talks".
You can't add a είναι to it.
Because 'μπαμπάς' means 'dad' and 'πατέρας' means 'father' I would say... So essentially, you'd be answering with the incorrect word in vocabulary terms. Even though the sense of who you're referring to is the same. To the app, it would suggest that you hadn't understood/learnt the vocab.