Since he has a Innova for long drives, I think a petrol car would make more sense? Or does it have to be a diesel?
In petrols, since you mention comfort, style and power, it would have to be:
2. I20 1.4.
3. VW Polo 1.6.
4. Punto 1.4.
Among the three the worthy *upgrade* from the Swift would be the Polo 1.6. But the waiting periods could be huge.
It would be better, if you listed out the equipment list your BIL wants on his car. Would make it a lot easier to list out the cars.