Recent vocabulary I've learned

Ab (father): أب
Um(Mother): أم 
Jad (Grandfather): جد
Jaddah (Grandmother): جده
Ibn (Son): إبن 
Ibnah (Daughter): إبنه
Zawj (husband): زوج
Zawjah (wife): زوجه
Akh (brother): أخ 
Ukht(sister): أُخت 
Ibn ukhti (my nephew(from sister)): إبن أختي <em>"It works whether your nephew is from your sister or brother's side, you can use (nephew) for both".</em>
Ibnat akhi (My niece(from brother)): إبنة أخي <em>"It works whether your niece is from your sister or brother's side, you can use (niece) for both".</em>

I would like to correct some words 

Jawz (husband) zawj 
Jawzat (wife) zawjah

Recent vocabulary I've learned

Ab (father)اب
Um(Mother)ام
Jad (Grandfather)جد
Jaddah (Grandmother)جدة
Ibn (Son)ابن
Ibnat (Daughter)ابنه
Jawz (husband)زوج
Jawzat (wife)زوجه
Akh (brother)اخ
Ukht(sister)اخت
Ibn ukhti (my nephew(from sister))ابن خالتي
Ibnat akhi (My niece(from brother))ابن اختي

zawj (husband )

Zawjah (wife)

For nephew we have two meanings 

1-son of  the sister = ibn  el ukht

My sister's son =ibn ukhti 

2-son of the brother =ibn el akh 

My brother's son = ibn akhi 

For niece we have Also 2 synonyms

1-sister's daughter =ebnat ukht 

My sister's daughter = ebnat ukhti 

2-brother's daughter = ebnat akh 

My brother's daughter = ebnat akhi 

Summary : for nephew we fix the word son ( ebn )and we change the next word according to if he is brother's son ( ibn akh ) or sister's son ( ibn ukht ) and the same in niece we fix daughter ( ibnah or ibnat here )and change whether sister's or brother's daughter .

to avoid confusion just translate it in literal meaning as sister's son = ibn ukht we only replace the first is the second and the second is the first as in french