Hi,
Yes, in your case a PULL down resistor from each input pin to gnd, 10K should be fine.
Where on the 33 is the D1 pin?
It is better that you configure the seat switches to pull down when closed, it is just a case of how you connect to the controller, not changing anything physical with the switch.
There is nothing wrong with polling, when you consider the controller speed, even at 16Mhz of a UNO.
Avoid using the delay() function.
Did you make a breadboard prototype before going to PCB?
Can you please post a copy of your schematic?
Thanks.. Tom.. 
