What if the MC's parents was killed by the mob and this family took him in. He could have been with a them a few years explaining him in the photo. As far as the sisters go since the MC is the one that put her hand there would that pass ?It basically has to be any kind of relationship where the words "mother" "son" "brother" "sister" "cousin" "aunt" and so on aren't even said in the game in any relations related to the MC. The other characters can be related to each other so long as they aren't doing anything together. The night time scenes with the sisters might be pushing it.
Your major problem is going to come from the Family picture in the main room. There is no way to construe that picture as anything other than a family.