The difference is not that big between "区别”and “差别“. "分别" kind of means respective and respectively or seperately.
分别 [fēnbié]
1. [leave each other]∶离别
分别了不到一年又见面了
分别 [fēnbié]
1. [separately]∶各自;个别
对他们应该分别对待
2. [respectively]∶分头,各自,不共同,不一起
会长和秘书长分别接见了他