Android Delivery Tracker App

I need a lightweight Android app that my six delivery boys can keep running on their phones while they work. The single goal is to let me open a simple web-based map (or an in-app admin screen) and see each rider’s real-time GPS position, updated automatically every few seconds, with their name or ID beside the marker.

Core requirements
• Android only — no iOS for now.
• Continuous, battery-efficient real-time location updates.
• A small backend/database so I can review each trip’s history later.
• Basic authentication: each rider logs in once with a unique ID and the app starts tracking.

Nice to have (but not critical for the first release)
• Status toggle in the app to mark a delivery as “Picked up” or “Delivered”.
• Push notifications if a phone goes offline for more than X minutes.

Acceptance criteria
• I can install the APK on all six phones, create the rider accounts, and immediately see live positions on a Google-Maps-style interface.
• Location accuracy within roughly 20–30 m in urban areas.
• Source code handed over so I can add features later.

Please outline the tech stack you prefer (Kotlin/Java for the app, Firebase, REST, Node, etc.) and how quickly you can deliver a working MVP.