What happens to current in a Parallel Circuit
Each laptop will draw the current it requires to run the CPU and peripherals. This will vary and may be much less than the 8 A specified - particularly once its battery has finished charging. The total current required will be the sum of the individual currents.
Note that the 8 A measurement is taken at the DC output of the power supply. The mains current will be lower by approximately the inverse of the input-output voltage ratio.
Assuming you have a great big 19.5 V PSU, it will have some rated current limit beyond which it will fail to operate properly, either by failing to give the full 19.5 V or by thermal shutdown.
Cable resistance will also cause the voltage to sag in proportion to the current. Other things to watch out for include over-heating of plugs and sockets.