How to implement a notifications on my webpages while any data insertion or updation occured on my custom tables
You need to accomplish with three module and rules, private message and custom module.

rules provide event, condition and action through which you need to set, events supports CRUD. Condition provides you to check condition has been fulfill and Event sends you private message to groups or personal mail / text message. 

Private message provides you send bulk message / mail through rules. Message itself can be thread.Private message has feature to count unread message to particular user.

Custom module to create event, conditions and actions for rules to custom table.