First of all, fuck realism, that's not why i'm playing avns.
Second of all, storywise it does make sense cause of the personality of the characters, Victoria doesn't get upset by almost anything(she wants everyone to be happy especially her sister) & it's impossible for Maja to get upset with Victoria so I think they will be able to share the mc without feeling any resentment.
Anyhow, these are the matchups which I think work best based on your list:
Victoria-Mila/Maja
Bella-Ayua/Nadia
Nami-Nia/Mila/Robin
Sasha-Robin/Nami
Nadia-Zara
Nick's Daughters
Sonya???
*I assume fans will probably seek out the Sasha-Bella pair the most, most popular I think.
*Nami probably fits with almost any girl out there cause she loves the mc the most, she's his sidekick.