React Native mobile app development cross platform

Our client has an existing mobile app currently on iOS and Android, that we'd like rewritten from the ground up using React Native for cross-platform release. More detailed information will be released to the successful developer once a Non Disclosure Agreement has been signed. The premise of the app is that it is used by freelance contractors to deliver advertising leaflets to residential homes. The freelancer accepts a job that is made available by administrative staff. The job data includes a Google map that highlights the streets the freelancer needs to deliver leaflets to. Once the freelancer commences a job, GPS tracks their progress and overlays it onto the Google map, allowing the freelancer to know what streets remain. The freelancer can pause the job, suspending the tracking, and resume again later. Once the job is complete, the freelancer submits the map gps data to admin staff, along with other data entered in a submit form on the app. Another requirement is that freelancers can have assistants, e.g. a parent takes their children to help deliver leaflets and they deliver leaflets to separate streets each. Once the assistants register, a freelancer nominates them as assistants. This needs to be stored so as to be available on multiple jobs, i.e. a particular user is ALWAYS my assistant for future jobs. Assistants can similarly commence and pause jobs. Their map data is combined with the principal freelancer's map data in real time whilst delivering, and is combined when submitted on completion. There are known issues with the current gps tracking. There are occasions where gps read fails, and rather than not record data, a straight line is drawn on the map from the current location to the original starting point, which is visually confusing and messy. This absolutely cannot carry through to the new version. The existing apps use web api calls to an Access database on a web server. The php api is already available, but will require extending for new functionality (this is not part of the brief though. we will take care of the api work). The long term goal is to eliminate the Access database and api, but as there is a very tight project budget it will remain in use for the time being. Instead, you will build a Firebase database that will store user data. Upon first registration by users an api call will create the user in the Access database, and the returned ID will be used to build a Firebase user so the two are linked. The app itself is quite simple, with basic registration screens, job list, active job (including map) and submit job. Detailed Crash Analytics are also required.