GST-Compliant Mobile Billing Application

Want to create simplest billing APK app for mobile phones use for my shop. My shop has 12 -20 salesman, 2-3 manager/cashier and me. It is a garment shop all products in 5% gst slab. Product rate are in multiple of ₹ 50 ragging from ₹50-₹1500. There is a commission for salesman whenever he convinced a customer to purchase of 0.5% wheather it converts into sales or not. Customer usually select products from multiple salesman .
App process is simple whenever a new customer come and select products for any salesman counter, salesman will generate a estimate number in his phone and example E101 and salesman will enter product rate and quantity. This estimate will automatically pop-up on all salesman and cashier/manager phone app. When customer move to other salesman counter other salesman can easily enter there products and quantity. At cashier/ manager counter a final copy of estimate will be printed on a bluetooth thermal printer 58mm/ 80mm. Commission of 0.5% with be generated according to final estimate created at cashier/ manager.

My requirement for app is simple
1) All salesman, manager and me are online.
2) each salesman can enter and edit only his product against his salesman ID in customer estimate.
3) cashier/ manager and me can enter and edit against any salesman product selection in customer estimate.