Same credentials in two different devices

Is it possible to use the same credentials on two separate devices (tabs) to access various follow-ups in commcare to reduce the time scale?

Yeah it's possible. Whenever you login into a device, CommCare will download all the user-data associated with that user and you can then submit various follow-ups. I'd also suggest to keep syncing periodically or maybe update the Auto-Sync Frequency to Daily for the app so that all the different devices remain in sync with each other.

Thank you, Shivam for your super help.

Dear @Shivam, as per your guidance we processed, the case list was updated in both the devices, we collected data with different follow-up questionnaires, unfortunately, the data not sent to the commcare sever.

unfortunately, the data not sent to the commcare sever.

Can you check whether the device was able to submit the forms? You can go to the saved forms screen and use filter by: only unsent forms. If the forms weren't submitted, you can press the sync with server button on home screen and that should send the forms to the server.
I'd also suggest checking the forms on server again, cuz it sometimes takes 5-10 minutes for HQ to show new forms.

One additional clarification:

If your goal is to share cases between the two devices: CommCare's case sharing mechanism (either through user groups or through organizations) will share data equally quickly between two devices as would logging in as the same user. A user can log into more than one device, but there are limitations to that approach (such as difficulties with the User Case concept) so we generally recommend having distinct users for each person using the app and sharing cases.