Well, I'm not here to actually 'define' the word 'complex'. Just saying that Sonny and Fredo were NOT complex. They were on the whole pretty easy to figure out.

But if you insist...see below from Webster's Dictionary:

Main Entry: 1com·plex
Pronunciation: 'käm-"pleks
Function: noun
Etymology: Late Latin complexus totality, from Latin, embrace, from complecti
1 : a whole made up of complicated or interrelated parts (Michael Corleone)

2 a : a group of culture traits relating to a single activity (as hunting), process (as use of flint), or culture unit

b (1): a group of repressed desires and memories that exerts a dominating influence upon the personality (2): an exaggerated reaction to or preoccupation with a subject or situation c : a group of obviously related units of which the degree and nature of the relationship is imperfectly known d : the sum of factors (as symptoms) characterizing a disease or condition

Apple