While filing civil suit, you should have prayed to court for direction not to alienate the property by sale or renting by the Defendant i.e. your brother till court proceedings. In the absence of such court order, he can lease out the property. Tenant's rights are not affected. However, you can claim damages.

The lease is subject to final decision of the court.  Forgery/fraud vitiates all contracts.  You can file IA and get injunction against such lease agreement by making the lessee a party.  As you have already engaged Advocate, he can be in a better position to advise as he is aware of the entire facts and outcome of the final judgment.

agreement is not valid during pendency of suit.

Section 52 of the Transfer of Property Act speaks about the doctrine of lis pendens. Section 52 reads as under:

“52. Transfer of property pending suit relating thereto. – During the [pendency] in any Court having authority [within the limits of India excluding the State of Jammu and Kashmir] or established beyond such limits] by [the Central Government] [***] of [any] suit or proceedings which is not collusive and in which any right to immovable property is directly and specifically in question, the property cannot be transferred or otherwise dealt with by any party to the suit or proceeding so as to affect the rights of any other party thereto under any decree or order which may be made therein, except under the authority of the Court and on such terms as it may impose.

File IA against rental or lease of the premises.