What if Harley and elias fell yandere over a childhood friend that grew up with them (lord help the poor soul if they both fell for the same person)? how different would it be compared to them going yandere for a stranger?
If it was just Harley who had the crush on you, things would probably turn out very different for him. It would depend on your personality, but if you were on the more caring and empathetic side then you would be Harley's safety blanket right off the bat. He would cling to you even as you got older and would be much sweeter on you than he would be if you had just met, since he can be standoffish and rude to people he doesn't know or trust yet. He wouldn't be nervous or frustrated to ask you questions he doesn't know the answer to because he knows you, he knows you're smarter than him--and more importantly, that you won't make fun of him for needing help. So he'll be much akin to a shadow at your back, always following in your footsteps and never leaving you to fend for yourself. Just be gentle if you don't return his feelings for you. He can handle being your best friend and not your lover, but he can't handle you hating him or wanting to leave him behind for a new life. He just can't. And you surely don't want to face the consequences if you ever tried to move off the farm or find a partner--in that aspect, Harley will not be gentle with how he handles such a betrayal.
If it was Elias who had a crush on you, then he would largely be the same person, but more empathetic to other people's feelings. You'd replace Harley as the only person whose feelings he actually cares about, and in turn he might be more ruthless towards him growing up since he'd now see him as competition. But if you make the effort to shield Harley or even just scold Elias for being cruel, he'll straighten up since he doesn't want to make you upset or be the reason you cry. But his crush would be very obvious and his flirtations will only become more commonplace as you get older, and the more you reject him the deeper into his obsession he'll go. Even more importantly he'll actively sabotage every relationship you enter, and if you ever end up showing signs of having feelings for his childhood friend, he'll move straight into kidnapping you because nobody else deserves to have you smile at them. Including Harley. He'd be a lot more brutal in how he isolates you, and he wouldn't even entertain the thought of letting you out for a little while like he would if you were just a stranger. You've known each other for so long, and he's loved you since he first laid eyes on you, and nobody knows what's best for you more than your best friend.
And if both of them have a crush on you, you'll have to endure a lifetime of being in the middle of everything. All the fights, all the tears, all the romantic affairs and half-spoken feelings...you'll never have a break when you're between the two of them, and when you get older and they distance themselves from each other, you'll have to choose which one you'd rather stay with because there's no way they're letting you go off on your own. They both see themselves as your protectors, not just from Elias' father but from all the other pains you've had to endure--and no matter what decision you make the ending will stay the same. One of them will try to assert themselves over the other, and the two of them will end up having to compromise. Elias will have to stay because Harley won't let you leave the farm, and Harley will have to deal with Elias taking up your attention and being the dickhead that he's always been. They'll both be frustrated, but if there's anything they can put their differences aside for, it's you--especially if they get to share a bed with you and see you smile at each of them every day, just like you did when you were children. And as long as you don't show too much favoritism, they'll be able to endure each other without a murder occurring.
