Since you have already filed a caveat petition, the court will not pass any order to stay the ongoing construction work without hearing your side.
As I said earlier, if you would like to contest the case, then you may not be able to proceed with the renovation work.
no doubt in the absence of any stay order, there is no restriction to proceed with the construction work but since you have not obtained proper permission from the local civic body or plan approval, this may hinder your process and the civic body may pass order to seal the building after which you have to run behind the authorities to break the seal.
Instead of messing up the things and also further complicating the things, it is always better to try for reconciliation with your brother and arrive at an amicable situation favorable to both the sides.
This will save your interests in the property and lot of money by avoiding the damages and litigation expenses.