you can just use one tong only (from Alam Flora) and for the rest of the tongs required, you can get from outside suppliers. very much cheaper

for the car porch, do we need to put steel at the bottom of the floor?

A note of interest:-
My place has become Motel de Indon 

Bed n Board   +  Cafe de Indon

bro,
saw your picture on the rear extension.
might be too late but it would be worth your while to have slightly higher wet kitchen area. do not have your roof to be aligned with the others. where possible, have it about a feet higher.
when you construct higher than norm, chances are your neighbour will need to construct lower than yours.
my problem was, i constructed mine first at normal height. my bloody neighbour constructed higher and his roof water spillover to mine!

what is the purpose of putting pvc pipes into the columns?

The major pillar/columm is still there, next to the door.
They are going to set up another 2 new corner pillar/columm at the new corner of the extended wall(Extreme left and right),
then put a new RC beam across joining the 2 new pillar and the existing pillar providing support. 

If the structural beam has been properly designed for, it can even go up to 20' clear span. No problem.

That could also mean that the 1st concreting of the column was not high enough. Thus a 2nd casting of the column and therefore you see the different in colour. All this is OK provided the column's steel bars are extended into the concrete beam.
However, if the column was stopped short and the gap between the top of the column and the bottom of the beam was patch up with cement mortar/ with bricks, then it is a cause for concern.

Am not sure what your contractor have done. I am not implying that what he has done is wrong or anything.
Introducing additional supports at the wrong location can be detrimental as the structure could behave differently from it original intention.

e.g. This is a case that I have come across in a house renovation project years back.
Some car porch are designed as a cantilever structure. Meaning that there is no support at the extreme end. (for aesthetic reason) The contractor then added a support as the house owner wanted to add a RC slab over the car porch. The structure collapse but luckily no one was around when it happened.

For safety sake, I really hope your contractor knows what he is doing.