Well I was the one who wrote the question but I can give you some of the ones I read...tho sadly I haven't found one as good as this.
There's
"An unseemly lady"-- mc gets isekaoed and is her fav charecters younger sister and their relationship is cute although soon she grows up and is in school and the older sister doesn't show up much but even then I like the romance too. It's decent. Nd the older sister is present atleast half of the time. I'll come back if I find anymore.
Can u give Me some you've read?
Oh I have another one that I really like maybe even more then this one. Though sadly it's not very popular and it's underrated as fuck
"Finding my fathers son": basically the mc Is poor and her mom is on her death Ed and tells her that her father is actually rich cause she slept with a noble so the mom tells her to find her dad ( Though the mc does have a stepfather and stepsiblings) so mc goes out to find her dad and finds out ...spoiler (her dad is on his deathbed) her dad was a hero who slayed a dragon on something and the dragon poisoned him and he was dying slowly. Anywhere he's happy to see his daughter even though he can't really move cause he's on his deathbed and basically a skeleton. I won't spoil everything bug like he gives her a sword that he used to kill the dragon and the dad can't use it anymore (I won't spoil why) but the sword doesn't really like the girl as an owner and she also didn't want to be stuck with the sword the rest of her life. The sword then tells her her father also had a son. So basically she's trying to find her father's son as the title suggest in order to give the sword to him (she also has narrowed down the candidates of who it could be but she doesn't know for sure they're are pike 3 or 4 candidates) There isn't really any major romance as far as I can tell but the story did make me cry and it's super good I recommend.

I want more webtoons that ar r like this with a.close sibling relationship
Please give me recommendations