Best way to go from existing React Web App and Android App => to Multiplatform App incl. iOS

upfront note that maybe relevant: I´m not a developer, but more app owner and project manager.So pardon in case I state something wrong and would be thankful for your corrections.

• Web App on React.js (at 80%)
• Native Android App on Java (at 80%)
• Backend is on Ruby on Rails, DB is on MongoDB

It´s a marketplace for posting and requesting articles. It makes use of a specific transaction process. It has common features like login over mail and facebook (facebook API), geolocation, map/places (google), push notifications (firebase), cam access, payment (paypal), chat (firebase).You may see it on: http://www.4free.online

Goal: I would like to add an iOS App now as well.

Generic question: What would you consider the best strategic way? Why?

1. React.js for WEB + React Native WebView for MOBILE
2. React.js for WEB + React Native for MOBILE
3. React.js for WEB + Flutter for MOBILE (design and logic)
4. Kotlin Multiplatform for ALL + Flutter for MOBILE (design only)

As per my current knowledge (out of theory only) my preference is bottom-up, being 4. the highest preference. Option 1. with React WebView is currently considered a temporary solution only in special to have iOS App fast available, not sure it may be a valid long term solution for mobile in general.

GENERAL FEEDBACK upon available options (incl. not listed ones)

I would appreciate general feedback and advise from you guys, who have years of practical experience and worked with all of the listed technologies and in best case even already have gone one or several of those paths and therefore are able to compare and evaluate the different options with their pros & cons you encountered.

SPECIFIC questions

In addition, I have some specific questions for what I currently believe would be a good approach:

Currently considering the following paths, per device type:

Android

1. Finalize 20% on Java
2. Kotlin Multiplatform

Questions

1. Is it worth to finalize first on Java, before moving to Kotlin?
2. How long will it take to go from Java to Kotlin Multiplatform for that kind of App?

iOS

1. Fast shot w/ React WebView
2. Kotlin Multiplatform

Questions

1. How long will it approx. take to create React WebView for that kind of App and used Services?
2. Is it benefitial to have first completely ported Android Java to Kotlin MP, before initiating Kotlin Multiplatform for iOS? If so, why?
3. How long will it take to have Kotlin Multiplatform for iOS developed for that kind of App?
4. In percentage, how much is shared and reusable based on Kotlin MP, how much is specific for iOS (Android)?

Web App

1. Finalize 20% on React.js
2. Kotlin Multiplatform

By the way, we are currently building up a team of 3-4 developers. In case of interest feel free to contact me seperately on this.

Many thanks in advance!
José