my Plot size is 30x60 feet, and my porch is 16.5 feet wide,
and 12.5 ft long (form small car) one side and 15 ft long (for big cars) on other side.
16.5 ft can have two big cars easily.
i have baleno (5.55 ft wide) and passo (5.5 ft wide) and the doors of both cars open with ample space, also when both cars are parked, thre is a lot of space between two for walking out of the porch.
I have also once parked corolla 2011 and passo, and still there is space to walk fom between the cars easily.
btw New corolla 2015 is 5.8 ft wide, if you park two corollas in 16-17 ft wide porch, it is a feasible option.