(I’m talking about transferring from CCC to UC.)
For Engineering-related majors, such as electrical engineering, computer engineering, etc… - there are lots of required prerequisite courses (such as math & physics).
So I was wondering that is it even possible to finish all the IGETC courses AND major prerequisite courses???(in 2 years in Community college) Because there are bunch of art & humanities courses, social & behavioral sciences courses for IGETC requirements… 
Nope not necessary, infact it is discouraged for Engineering majors.
It depends on major by major.
EECS, for example, doesn’t accept IGETC. You need to go to assist.org and complete everything it says you need to complete.
Assist.org will generally point you in the right direction for any major.