There will be no blood relationship between MC and LIs even considering the ep 12 cliffhanger. Nyx (the dev) has said many times that there will be no incest in the game, she has also cleared all relationships with Patreon moderators who don't allow incest.
Having said that the known relationships between the characters are Emily is MC's mother, Melissa is Erynn's mother, Adrianna is mother to Layla and Alexis, Layla and Alexis are sisters, Coach Mike is father to Cora and Nikki, Cora and Nikki are sisters. Likely but unconfirmed relationships are John being Erynn's father, which make Erynn and Iris half-sisters, Ximenia being Val's mother, Gabi being married to Santiago (MC's father).