Customize web portal and android application

I have bought one school management system with Android application. I want to do some changes in this. Below are few major changes and will explain all the changes in detail after confirmation. 1. I want this to enable for multiple schools. So there will be one admin panel from where schools can be added and after that school will be able to login to the system. 2. Only Admin department and Account department should be able to login to web portal. Teachers, parents and students should only be allowed to login through mobile application. Login should be based on mobile number verification only like Whatsapp. 3. There should be three distinct mobile application, one for the teachers, second for the parents and third for the students. 4. If there are multiple children for same parents then there should be option for parents to change the student in mobile application. Similarly, students should also be able to change profile and teachers should have an option to change class. 5. Current layout and design for Mobile application as well as web portal needs to be changed completely and new design will be provided by me in Angular JS. This theme has to be used in web portal and mobile application. 6. I don't want to use all the modules from this. I only need Attendance, Time Table (Class Schedules), Class Exam, Online Exam, Students, Parents, Class, Subject, Events, Assignments, Vacations, Messages, Fees. 7. I also want to integrate payment gateway. This will be at free of cost to all the schools for particular time period and after that I should be able to configure charges for every schools and that will be on monthly basis based on the number of student. For example, if the charge is configured as INR 1 per student per month and there are 500 students in a school then after free time period, school should be charged for INR 500 for first month. And this payment can be made through admin account of that school only.