In your case, your son should call his cousins who are elder than him "表哥". As for the one who's at the same age...you'd better figure out who was born earlier, haha. Even if he was born 1 minute later than his cousin, he should call him "表哥". My sister was born several hours earlier than my cousin, so my cousin has to call her “表姐” even though they were born on the same day~ Hope this will help~

Rule of Cousins :) The Chinese term of cousin is the combination of two characters. 1. First Character：whether 堂（tang）or 表（biao） Golden rule is if the cousin shares the same last name as your child, your child can refer he or she as 堂（tang），otherwise 表（biao） So it's the specific parent of each child involved that matters. If and only if they are both male，use 堂（tang），otherwise 表（biao） In your case, as long as they are your sister's children, you would want to use 表(biao), as your sister is a female. 2. Second character: choose between 哥（ge）/兄（xiong），弟（di），姊（zi）/姐（jie），妹（mei） 哥（ge）/兄（xiong）: both refer to elder male cousin, 哥（ge）is more common，兄（xiong) is more formal; 弟（di）: younger male cousin; 姊（zi）/姐（jie）: both refer to elder female cousin, 姐（jie) is more common; 妹（mei）: younger female cousin. So in your case, your two elder nephews are the 表兄（biao xiong）/表哥 （biao ge） to your son，and the youngest nephew is whether the 表哥（biao ge）or 表弟（biao di）to your son，depending on their age Since your son has at least two 表哥（biao ge），you can distinguish them by putting an order before the term. It usually goes in numbers: eldest-大（da）, second-二（er），third-三（san）... Consequently, Calum is your son‘s 大表哥 （da biao ge）, Kyle is his 二表哥（er biao ge） and Ethan is his 三表哥（san biao ge）if Ethan is older than your son，表弟（biao di）if Ethan is younger than your son If you want to refer to three of them as a group--- If all of them share the same term, use that term. So if Ethan is also a 表哥（biao ge），you can use 表哥（biao ge）； if Ethan is 表弟（biao di）， you can use 表兄弟（biao xiong di）； if one or more of them are female， you can use 表亲（biao qin），it means cousins in general I hope I didn't make you confused : )

for the older two shall call 哥（ge), for the younger one shall call his name is ok!

补充： 堂哥：一个人父亲的兄弟的儿子,如果都按照传统随父亲姓的话，堂兄弟应该是同姓的； 表哥：一个人母亲的兄弟姐妹的儿子，或者父亲的姐妹的儿子。大部分情况下，表兄弟的姓是不同的 In your case, you call Calum & Kyle 你儿子的表哥，Ethan is 你儿子的表弟。但你儿子如果称呼这几位时可以直接叫他们名字或者叫“哥哥”“弟弟”。