Hari was around 28 when she went back in time and was adopted when she was 8 or 9 so that's about 20 YEARS of Hari being his sister. And you may say that she was mistreated and it therefore does not counts as a sibling relationship but Hari herself states that they had a good relationship before she died (when she remembered how she would be sleeping and he would quietly sit by her side) so as far as I'm concerned Hari sees him as a brother. Eugene on the other hand may not see her as one as he hasn't known her as long and wasn't even with her for the majority of that time but after having all that history this is nothing but strange to me. But I'm not gonna hate on It because I'm pretty sure we all saw it coming
They don't have to have a sibling relationship, what matters is how Hari viewed them. She may have compromised to be their sister because she felt guilt/melancholy for the dead parents (the past and now) so she took it on herself to watch over them even tho they rejected her, plus she said it herself that her greatest fear was loneliness when her mom died so she preferred to have them around her, in that way she might have already subconsciously or not considered them family.
i don’t care what anyone says i love eugene x hari with all my heart also stop with the incest shit they’ve never had a siblingly bond cuz they only lived together for what a year together as kids and since then they never lived together for 6 years they never had something like a sibling relationship to begin with you can’t say that they are siblings just cuz she was adopted into the family