Can i charge 2 li-ion 12v bateries in Series?
1) The pros of serial charging for you would be the convenience of not having to rearrange your battery configuration to parrallel every time you want to charge them.  The biggest con in serial charging is the potential for the two cells to become imbalanced.  This happens when they have a different internal resistance and thus they charge and discharge at slightly different rates.  Over time this can cause a serious problem.  Imagine that the first battery in the series discharges a little faster than the second battery.  When your device (laptop) that measures the level of charge of the batteries tells you the batteries are empty, it is measuring the voltage of the two batteries combined and at 18 volts it says "empty". However, since the first battery is emptying faster it might be at 8.5 volts and the second battery at 9.5.  The same problem can happen with charging.  As a result you can end up destroying a battery or a battery blowing up etc.  

lithium ion chargers that charge in series monitor each cell as they charge and provide a balancing feature to correct for the above mentioned potential problem.

From the research that I have done, it is generally safe to charge lithium batteries in series when it is a low number of cells in series, less than 4 or 5.  In your situation you are using two 12 volt lithium batteries which is 3 cells in series each - so 6 cells total in your 2 batteries.  Probably too many to safely charge in series without monitoring them.  

However, if you checked the voltage of each battery at the beginning and end of each charge cycle, you might be OK because you would catch each battery before it got seriously out of balance.

2) Sorry I don't know the answer to this question.