Shorter answer: The romantic route is with Mallory and Eleanor. The relationship with the other girls is more sex.
Longer answer, with a bit of a spoiler:
The game has 2 main LIs, Lucy and Mallory, and 4 routes, 2 for each, one with incest and one without. The route with Mallory with incest is the most romantic and the only one with the older sister Jessica, which is more focused on sex. However the main romance, in my opinion, is with the younger sister Eleanor. Lucy's route doesn't have much romance.
The other MCs are Lucy and Eleanor. Eleanor has far more scenes. Their scenes without Tom (the default name for the male protagonist) are with each other or with Rose, Mallory and Jessica, yes there's sister/sister action. However, the scenes involving Eleanor are avoidable. The ones between Lucy, Rose and Mallory are not.
90% of the negative feedbacks are about Lucy. You have to go further in the story to know why she tries to stop Tom from having sex. However, she actually only stops ONE girl from having sex with him, Rose, and it doesn't last long. He has sex with other women anyway, but most of them are in the non incest route.
The NTR is with Lucy and Rose. 4 scenes early in the game, before they have any relationship with Tom. You can choose not to see them, but they happen anyway. Rose is a friend with benefits and a fuck partner. And Lucy you can avoid and do the Mallory route, which I think is the best one. But since Lucy is an MC or can be just a friend, and Rose is not a LI, technically there is no NTR in the game.
So, as I said in my previous comment, the game has a good romance with the younger sister and I think it is worth it. I recommend doing the Mallory route, which makes Lucy just a friend. But if you don't like seeing some lesbian scenes, I recommend avoiding it.