If you haven't read Living with a Retired Demon Hunter , it is the definitive recommendation for this search. It perfectly captures the "Monochrome" (melancholic/subdued) atmosphere and executes a "Top" tier narrative about finding family in a hostile world.
But Elara couldn’t. Not since the monochrome came. Not since their parents walked into the White Wood and returned as outlines — hollow, smiling, empty. living with sister monochrome fantasy finishe top
(Assuming this is the target title, as it is the most prominent "Living with Sister" fantasy series) If you haven't read Living with a Retired