1. Yes, you can relinquish your shae in favour of your brother.
2. However such relinquishment occurs without any monetary transaction.
3. Hnece to get money out of your share you need to execute and register a deed of sale where consideration amount for the transfer of share is mentioned which can be consisting of both present and future transaction of money.
4. Gotst deed can also be done but again you can not mention any monetary transaction therein.
5. Though sale deed is best suited but it attracts more stamp duty then the release or gift deed.
6. If he pays the whole amount ( unofficially)then go for gift deed.