Chu x Pet

The protagonist is a high school student whose life changes drastically when one day his mother tells him a man has proposed to her and she asks for his blessing. Being raised entirely by his mother he accepts so she can be happy.
Then the day he finally meets his new family he shockingly finds out his new sister is the school's student council president and popular student Sakuya, as he now forms part of the Aotsuki family.
Sakuya has an unnatural fixation on making him her "brother pet". His cousin Shuri feels threatened by Sakuya taking the protagonist's sister spot and his childhood friend Kotori hates him for some reason.
Eventually he is forced to run as the next student council president. Sakuya, Shuri, Kotori and Sakuya's twin sisters Yuzu and Kana will help him in his campaign.
Who will the protagonist choose to help him in the election?