1) If our hybrid batt is fully discharged, no way we can start our PC. Right or wrong? (Note: Case of Hybrid batt still functioning/OK, but only fully discharged due to car is not being used or start in a very long time)

No, you won't be able to start your car.

2) Can our PC be able to START back if it is not being used in ONE month time? (PC 12V batt charge can last/hold for how many days before it is fully discharged? Same like normal car which we must start at least once in a week?)

Should not be a problem provided your 12V battery is healthy and hybrid battery is at near full level.
3) What can we do to our PC when we r oversea for mths? Pls dun ask me to sell it off or renting to frens I love my PC very much. Need to disconnect 12V batt? How abt the programming/memory side )

Ask your family/wife/husband/GF/BF to drive your car for 30 mins once a month.

4) Is PC 12 V batt is not the same with normal car 12V batt? (Since it is located under rear passenger area or car's cabin)

PC 12V battery is almost the same as normal car except it has a duct connect the battery to outside to dissipate hydrogen generated by lead acid battery. if you replace the 12V battery with normal one, you may in the danger of hydrogen explosion

1) if fully discharged no we cannot start.
2)I don't think it can last for 1 month
3) Prius n Prius c 12v battery not same the price for it is rm 500  . No idea what difference . At least can last 5 year but Prius owner on Malaysia have change it after 1 year
4) u can try jump start it if cannot call Toyota to start it for u . But u can charge the battery full first before storing for 1 months put on D n press throttle a little bit with hand break down n holding the brake or can Ho out drive above 70km/h for few minute also can