Simple Android and iOS app for internal use in a tiny company

We are a small tour agency. We run walking tours and each guide runs several tours on the same day. When we start each tour, we pass the tour-guide’s phone to the tourists for them to fill out a little survey that has 6 questions ( 5 of them are static (1)Name, (2)email, (3)country of origin, (4)hotel name, (5)how did you hear about us, the last question is dynamic -We change it from time to time to make market research-).
At the end of the day, the guide clusters the records and exports them as CSV file to his phone.

We want to upgrade the App:
* Currently it only works in Android. The new App must run both in Android and iOS. We are a team of less than 20 guides. We do not need the app to be published to any store.
* We want the new App to get its settings and pre-sets via a GET call to our API every time the App is opened. The answer will be a a JSON with the following format:
---- settings:
-------------------- password
-------------------- token
-------------------- GET_base_URL
-------------------- POST_base_URL
-------------------- file_ID
-------------------- sheet
---- countries:
-------------------- list of countries
-------------------- pre-sets
---- hotels:
-------------------- list of hotels
-------------------- pre-sets
---- channels:
-------------------- list of channels
-------------------- pre-sets
---- question:
--------------------type (single choice, multiple choice or text field)
-------------------- question text
-------------------- options (in case it is single or multiple choice)
-------------------- other_option (yes or no, to give people a chance to have the field "other")
---- options:
-------------------- email_type
-------------------- Question_type
---- tourist: (information from the booking system with preloaded info about tourist)
--------------------{ name1
-------------------- email1
-------------------- hotel1}
-------------------- {name2
-------------------- email2
-------------------- hotel2}

* Currently the App exports the records in CVS file. We want to keep that, but we also want to POST the exported records in JSON to an URL that will be provided in the SETTINGS JSON
* We want the new App to have some pre-set answers to some questions. e.g. One of the questions is "Where are you from?" We want to have the text field to be filled by the tourist (with auto-suggest from the list provided by the JSON. As people type a list of suggested answers appears), but also we want some buttons with some pre-set answers (most of my tourists are from USA, Germany, ...). The list of suggested answers and pre-set options will be provided by the JSON via the GET request.
* The last question is dynamic. Currently it has to be changed in the phone of every tour guide, which is a nightmare to update. I want the last question to be updated every time the app is opened via a GET request. The settings for the last questions are the following:
** Type of question (single choice, multiple choice, text field)
** Question text
** Options to the question (in case of single or multiple choice)
** "Other" field (in case we want to give people the chance to give an answer different than the one in the options)
* The app should be able to load even if the phone of the tour guide doesnt have access to internet. So it should be able to store the last settings.

I am attaching:
1. An explanation through images and screenshots on how the current app works
2. An explanation through images and screenshots on how I imagine the new app. It contains details on how the CSV file should be
3. JSON file example of what you get via the GET call
4. JSON file example on how the data colleted should be POST
5. The files of the current APP
6. The APK of the current APP