I have 10+ years of experience with Java and C++ and 5+ years of experience with Android app development. I have worked with SQL Server and NAS filesystems in the past.
I am listing the deliverables for your reference:
1. SQL Server DB with teacher, student collections and any others if required
2. Backend (Preferably Django) to expose the data in the form of RESTful APIs
3. Three Android apps, one each for students and teachers, and one for creating and uploading recordings to the server. The teacher and student apps, other than performing their intended functions such as triggering and grading, can also double up as their admin consoles.
4. Admin web module for account creation/deletion and superuser access.
Let me know if I missed anything, and feel free to message me to discuss this further.