You can ask RERA to direct  builder to give details of other allottees to these homebuyers so that an association of allottees can contemplate action under Section 7 of the Rera Act to complete the project

vide section 7 of RERA a complaint can be filed against the builder seeking revocation of his RERA registration

if the authority passes an order of revocation of registration of the builder then under s.8 the RERA authority may either take up the incomplete project and have it completed through another builder or through the association of flat buyers

so if the flat buyers want to take up the remaining development work then they can resort to s.7 and 8 of RERA. However this is the central act. so please confirm if there is any amendment by your state to these sections. a local lawyer should be able to tell you

also the flat buyers can approach the NCLT as financial creditors for initiating corporate insolvency resolution process of the builder company [assuming that the builder is a company] and if the builder is admitted to CIRP, then a resolution professional will be appointed who will invite bids from prospective parties for completing the project and/or reviving the builder company. This party is called the 'Resolution Applicant'. If the RA is selected and his resolution plan is approved then that RA will take over the pending project and complete it. 

Yes you can approach RERA for remedies in this regard.

Section 7- Revocation of registration.  The promoter makes default in doing anything required by or under this Act or the rules or the regulations made there under.

Section 7 of the RERA Act empowers the RERA Authority to revoke the RERA registration on receipt of complaint or suo motu or on the recommendation of the competent authority after being satisfied that – a) The promoter makes default in doing anything required by or under this Act or the rules or the regulations made thereunder, b) The promoter violates any of the terms or conditions of the approval given by the competent authority, c) The promoter involved in any kind of unfair practices or irregularities. d) The promoter Indulges in any fraudulent practices

MAHARERA Issues Revocation Notice to 563 Projects Under Section 7 of the Act. 

Section 7(1) of the Act covers the revocation of registration of a project'

Section 7(2) outlines the procedural aspects of revocation

Section 7(3) empowers the Authority to impose conditions on the promoter instead of revoking registration.

If the authorities want to cancel a project's registration, they have to first give notice to the developer explaining why they want to do this. The developer has a chance to explain their side of the story. If the developer doesn't follow the rules or violates terms again, their registration can be canceled.

Alternative to Revocation - Imposing Conditions:

Instead of completely canceling the registration, the authorities can set specific conditions for the developer to follow. These conditions are meant to protect the people who have bought units in the project (allottees). The developer must follow these conditions, or they will still face problems.

Yes you can get a rera order

Dear client, A buyer can request possession of a property before the completion of construction, but it is illegal to take possession without a valid completion certificate. The builder cannot force possession if the local town planning authority does not issue the OC or CC. The OC is a document issued by local government agencies or planning authorities after a project is completed.

You can also get compensation from the developers for delayed in possession of the apartment under RERA.

- Since, the matter is sub-judice before the High Court for the said property , then the RERA cannot pass an order to handover the possession.