Not my own mom or sis, but I get where you're coming from.
The more wholesome, loving, kind and innocent she is, the hotter the contrast is to see her getting absolutely railed in front I'd those she loves. Especially if her screams for help, muffled by a cock brutally trying to fuck the voice out if her, get ignored and she has to watch as the people she love most of the world, the son she almost died bringing into the world or her protective father, smile and openly start to jerk off to it.
Idk if them being YOUR loved one makes it especially hot for you, but I do get the urge every time I see an innocent girl who looks like she'd blush just from hand holding, or a wholesome pta mom busily Cleaning up after her kids with a happy, loving smile that could light up a room.