Hello friend,
i have gone through your project detail carefully, you need android studio coder, yes we have, you have app you want to add sub categories,' I have mobile app (Hybrid, Android, IOS) , php and backend skill.
We are a 10 year old IT company with highly skilled designers and developers to work on php, Mysql, Jquery, Wordpress, OSC, Magento, OpenCart, Mobile development, iPhone, Responsive etc.
It would be better if you come to have a close discussion over chat .
Best Regards
Harpreet Singh