My brother follows the same route and has a manual 2 door Mira. Mileage above 20 kmpl is achievable if you manage to keep a light foot and avoid those infamous office hours on the highway. Automatic 4 door Mira (I have one) should give you 16-18 kmpl but it lacks woefully on torque (frustrating in traffic hours when you need to pick up speed quick) and is going to hit the bumps in PWD unless you add spacers or larger tyres.
Swift is going to consume more fuel but will give you power and that look. Honda City's consumption is probably around the same ball park as swift if not slightly higher. It has a softer suspension though compared to the other two in my opinion and that helps on the slightly longer drives. Fuel costs may not be too big a concern in today's petrol rates but petrol will rise again. If you have a larger family car already and would like to save around 2000 a month in fuel costs, buy a Mira, if not, I would say City or Swift are just about equally good if you add pros and cons for both.
Room as in space? I doubt it. Swift is the most cramped of all 3. I have driven all 3 and found Mira with most rear and front leg room, followed by Honda City and lastly Swift.