Whether you took possession of the property after buying it?
If so and if the property is under your continuous possession and enjoyment ever since the date of purchase, then the so called transactions between Reddy brothers without possession would be considered as a nominal and sham sale deed.
The title on your name by the virtue of the registered sale deed in your favor is legally valid and if the Reddy brothers are staking claim, you can challenge the same on the basis of the documents supporting your claim