@omegaxis1
The same things may be seen as creepy or cute depending on context and author.
The ML from viridiscent crown is not forceful about is love, is quiet about it and his sister always liked him so his attraction can be seen as cute because it is harmless, he also asks for consent on everything he does and doesn't try to control her sister.
The brother from this one is hated by his sister, doesn't actually love her but has actually hated her for 1.5 lives. After Aria suddenly developed into the "perfect lady" he is now attracted by her and he thinks he has nothing to make up for and can simply get into her life and decide who she can and cannot see to remove his competition.
Context matters for this kind of thing, "incest" is disgusting when you are disgusted by the human behind it, if the two characters are in love it becomes just a bump in the road.
PS:this is for not blood related incest, if they are blood related it's always a big nono for me