Is it possible to convert 19.5V 3.33A to 12V 5.5A?
The answer to your header question is NO!

Input 19.5x3.33 = 64.935 Watts.
Output 12x5.5 = 66 Watts.

So your new output power is higher then your input power which is against the law of conservation of energy.



But according to your question details your equipment requires only 48.5 Watts. 
That is do-able but only if your buck step down converter (or converters) has/have at least 75% efficiency. 

But as Chris Stratton already said: it is better to use supplies which are dedicated for the circuits. You will be spending time and effort on something special, whilst there are cheap, ready made solutions. The idiom "penny wise, pound foolish" comes to mind.