Zombie apocalypse romance was released originally as a mini series with 12 short books

[Charissa]

Two girls are found in a department store by a group of brothers and three younger sister they dress as a boy. The group ends up leaving the store due to zombies attacking. The boys decide to stick with the girls and go south. One of the joys constantly tells one of the girls to stay by him and only him. The group faces lots of disasters even finding out the little sister Paige is immune to zombie bites. They hide in a farm house at one point when Paige is sick and try to find meds in a town but the town ends up being cult like. The group picks up a sister and her younger brother who are the children of the cult leader.

[Mai]

This series by Rachel Higginson came up in a search and seems to match your description:
https://www.goodreads.com/series/1152...
Book 1 is Love and Decay, Episode One.