1. Native iOS followed by Native Android
2. Flutter
3. React Native
4. Capacitor
5. Microsoft toolkit of the day
I may soon embark on such a task with such a small team. I am leaning towards #1.
Something to think about is all mobile apps come with the typical boilerplate. Think about a screen that displays the results from a REST call. You will need to create the screen for the Android app using either XML or Jetpack Compose frameworks. The iOS will need to create a screen using storyboards or SwiftUI frameworks. That is a lot to maintain. With Flutter you create the screens just once in Flutter and the only framework choice is Flutter. Now at some point in the future when the REST call adds a new field you have twice the work to do with native solutions then you do with Flutter to add it to your screen.
I would also like to correct misconception about Flutter. Flutter doesn't eliminate the need to do cross platform development. You still need to know the native tooling, native build cycles and native programming languages if you want to get a Flutter app out the door.
If you are a small teams looking to get something out the door, all of these are points in favour of Flutter. It works better for teams will constraints such as team size, budget and time.