Not being confirmed in CPSU

you will not be placed junior to subsequent recruitees.

But this will hold in case you were on probation.  Not if you were, ad-hoc, daily wages, apprentice etc.

use RTI and seek entir enotic leading to this confirmation.

When you have a counsel and paid for his services, discuss about these developments with him for further lawful process.

As advised by Shri Sudhir kumar file RTI Application.  The three issues identified in your post is shown in brackets.  Let your advocate file RTI Application in his own name and seek information as per application format if any prescribed and with RTI Fee.

(After completing one year of probation management extended probation of all 8 officers without any notice and again after six months they did the same)

1.Please inform specific reasons for extending probation for another six months for all 8 officers, and provide such specific rule and regulation that empowers for extending of promotion without stating any grounds.

(After completion of two years and 3 months of service they gave a show cause notice to 7 officers that as there was only one post and 8 officers selected so why not your service should be dispensed)

2.Please inform the specific major and minor irregularity pointed in show cause notice dt....to 7 officers and the concerned rules and regulations under which SCN was issued without specifically pointing out any major/minor irregularity in functioning for ....months, ...months even after promotion.

(Management confirmed the appointment of our junior batch 5 officers appointed in November 2015).

3.Please inform as to the procedure of confirming juniors, when the seniors were not confirmed and probation was extended without assigning any reason.  Please provide entire office notes prepared for that confirmation, and issues discussed about the old staff that were not confirmed even after extended probation.

.(Please advise further if court can take cognizance in this fresh development to stayed our juniors confirmation. )

(Now we will be treated as junior against our juniors)

4.Please provide the extant of such rules and regulations in Consideering  seniority in between the old officers that are still continuing on extended probation and those junior officers which were confirmed when seniors were continuing on probation.

What are the chances that we will be confirmed as permanent by court order.

5.Please provide such office notes on record for confirming juniors whereas the seniors are serving under probation and the matter is subjudice.

Yes, the facts posted suggests a higly arbitrary stand. Make use of the RTI to gather the complete facts and bring them to the notice of the Hon'ble High Court. In the present situation your advocate will the best person to guide you further.