How do you pronounce cuius?
It seems to be pronounced differently. 'quis' is /kwis/ but 'cuius' is /ku jus/, not /kwi us/ (and 'cui' is /ku i/ not /kwi:/).
Why is G sometimes pronounced as J?
The letter “g” makes the /j/ sound when followed by an “e,” “i” or “y” in a word that is often derived from Greek or Latin (these languages do not use the “j” symbol to represent the /j/ sound).