score:3
It's fairly trivial to check those two airlines websites for the cabin baggage allowances:
Jetstar Cabin Baggage Allowances - 1 small item (includes laptop bag) plus one main item (56cm (height) x 36cm (width) x 23cm (depth)) for a total of 7KG (more weight is included with business or higher class tickets).
TigerAir Cabin Baggage Allowances - 1 small item (examples seem smaller than a laptop bag) plus one main item (54cm (height) x 38cm (width) x 23cm (depth)) for a total of 7KG.
Also, does someone check the weight of the bags?
That entirely depends on the agent checking you in or issuing your boarding card - I personally have only had my carryon weighed a few times in my travels, and then generally its been on cheaper tickets and with budget airlines.
In this case, as both airlines prominently display their charges for excess cabin baggage, and charge for checked baggage, then you will probably have your bags weighed as that is a revenue stream for them.
what kind of fine most airlines impose
The cost of overweight hand luggage is included in the above links - Both Jetstar (scroll down for cabin baggage rules) and TigerAir (on the above link) require overweight or oversize cabin baggage to be checked into the hold, which incurs a charge for both airlines.