Develop Android and iOS app that is 1 on 1 online Chinese lesson only for student side

Hi, we. are looking for developers who can develop iOS and Android app.
Our service is 1 on 1 Chinese online lesson.
We've already developed Web service.

The web system function already has Students, Tutors, Admins role.

But we are going to develop the app only for STUDENT side.
App has to be compatible with all of our web system which is student and tutor, admin.

Expect Student App Functions
*Sign up and Sign in
*Dashboard (Showing booked lessons and previous lessons for writing reviews)
*profile
*Book lessons (Checking tutor's profile and available lessons)
*Video and voice call system (using API)
*Lesson history
*Payment
*Setting (Language, timezone, email, password)

We wanna know how long you need and how much is the cost.
Thank you for your considerate.