For Saber's case they are from different time/different choices (like using Excalibur or using Rhongo,...) and summer versions.
For Sakura's case, only Parvati and Kama are pseudo-servants while BB, Kingprotea, Passionlip, Melt (and Kazuradrop & Violet) too are from CCC. MoonCancer BB is originally a part of Nurse Sakura AI and is the creator of Alter-Ego Sakura Five. BB also has a summer version when she's supposed to be Foreigner but yeah at the end her class is still MoonCancer.
I forgot the reason why Eresh and Ishtar happen at the same time, tho.