I have always been confused about calling "位列第二的弟弟/大弟弟/哥哥," which were translated to [Second brother/eldest brother/older brother]. Anyone has a better way to differentiate them?  

You can refer to two brothers as "younger" and "older", or as "the little brother" and "the big brother". "Elder" is acceptable but a little out-of-date. When you say "little" and "big" you are referring to age and not height or weight.Jun 4, 2014
== Is it little brother or younger brother?
When you say 'younger brother' the listener will understand that he is younger than you. When you say 'little brother' you are implying that your brother is not only younger than you but he is a little boy. He is John, my younger brother.
== What is another way to say brother?
homeboy
bro.
brother.
buddy.
fellow gang member.
homie.
neighbor.
== What's the meaning of youngest brother?
One's younger male sibling.
== Synonyms for Younger brother · kid brother · little bro · little brother · baby brother · baby bro · youngest brother · young brother · younger sibling.