I've also read plenty of other webtoons and I can say that the panel layout and the way speech bubbles are placed are sometimes confusing.
The art also suffers of "same face" making difficult to identify at first glance which character is which.
The terms are hard for me because they sound very similar to Korean names so, I get confused when the same term is used for other character.
I agree with you regarding the art suffering from same face syndrome but I think at best the two main characters are easy to identify .
Regarding speech bubbles, as a general rule in korean manhwa / webtoons you start from left to right like it is in the west, and you begin with the highest balloon and work your way down, if the characters are talking back and forth you follow the same rule but alternate between the two characters.
Here are a few respectful honorifics to get you started:
Noona -> "Older sister" usually used by males to refer to older females, not necessarily related to them (it's similar to the japanese Onee-chan)
Unni -> "Older sister" used by females to refer to older females, again blood relation not neccessary
Hyung -> "Older brother" used by males to refer to older males, follows the same rule as 'noona' (similar to the japanese "Onii-chan)
Oppa -> "Older brother" used by females to refer to older males, no blood relation required
Sunbae -> "Senior" used by both male and females to refer to people of higher position at work or school, (it's similar to the japanese "Sempai")
-nim -> I believe is sometimes added to Sunbae, it is a respectful honorific