Registration of flat before being obtention of Completion certificate and Occupancy certificate by B

Project being completed about 80%. water and Power yet to be obtained from competent authorities except for Borewell and Generator availability in the project. The Builders status under RERA presently expired during feb.2019 after extention on feb 2018. Due to the pressure from purchasers the Builder is ready to provide symbolic possession duly registering the sale deed. With an assurance to get the possession in the company's letterhead upon completion of project after six months from the date of sale deed.A few purchasers have got the registration done also got the access to the flat. Our concern is that 1.whether the purchaser get protection duly getting registered with out completion certificate from competent authority. 2.whether symbolic possession given/assured in the sale deed is valid in the eyes of law. 3.if builder donot provide completion/occupancy as conveyed whether we can file a suit either with RERA/Consumer Court. 4.The builder also not able to complete in full within 30 months now under the grace period. 5.is there any Avenue to claim rent reimbursement from Builder for those stay in rented houses since unwilling to get registered even after payment of 95% of the flat value. 6.if property got registered in our name whether we will be able to claim the entire money paid to builder along with interest. Lastly whether RERA expired projects are comes under the purview of RERA act. This project started during April/may2016. Please clarify.