Q: Two iPhones 4S and 5 have the same Apple ID. All incoming calls and TXT messages are being shown in both the phones. How to avoid that?

Not use the same Apple ID for both devices. As you can see it causes a great deal of problems. Create a new ID for the one and if you need to share content, then you can use Family Sharing, but trying to use the same Apple ID for both devices and keep things separate is difficult at best.

Calls on two phones:

Partial solution on both phones:

Settings > Phone > Call On Other Devices > OFF

Best solution by far <<<

Get separate Apple IDs and use Family Sharing.

https://support.apple.com/en-us/HT201088