Sales and inventory management system - HELP

Ask lang po sana kami ng help or guidance.

Pinapagawa po kasi kami ng Sales and Inventory Management System and kailangan po namin i-integrate ang 3 branches into 1 database. Gusto po sana namin na real-time or updated ang sales at inventory ng bawat branch.

Paano po ba yung tamang way ng integration?
Any tips, explanation, or sample idea po will help a lot.

Thank you po in advance!