I'm having a hard time searching for this, but is there a list/pdf of 3.5 curses?
I'm looking for the curse that allows the caster to harm someone close (close relation, not distance) to the target when they are attacked.
By far the most notorious such effect is love’s pain, a 3rd-level corrupt spell1 from Book of Vile Darkness. As far as I know, it is also the only such effect—these kinds of things are really hard to adjudicate in D&D and often kind of irrelevant to how most of the game is played, so they don’t see a lot of attention. Book of Vile Darkness is pretty much the only place where they’d go out of their way to provide it—and love’s pain is the only such effect in that book.
To be fair, even love’s pain doesn’t quite match your request. It doesn’t actually do damage-redirection. And it doesn’t care about familial relations. But what it does provide is almost-certainly the most impossible-to-avoid damage in the game.
Specifically, while the subject of the spell must be within Medium range, and must be vulnerable to a mind-affecting effect, the spell doesn’t do anything to the one you cast it on. Instead, it deals up to 10d6 untyped, SR: No, Saving Throw: None damage to the subject’s “dearest love.” The spell description only notes antimagic field that can protect that person—distance, their own immunity to mind-affecting effects, spell resistance, saves, damage reduction, energy resistance or immunity, none of these things matter. The loved one can be on another plane entirely and the damage is still going through. Nothing in the game provides that kind of reliability.
Now you may be thinking “sure, but you need access to their dearest love”—no you don’t. It’s not who they love, it’s who loves them. And if you’re thinking “well, OK, sure, but you still have to find someone who loves them more than anyone else,” you aren’t thinking like an evil spellcaster—and yeah, this is very much an [Evil] spell. The spell doesn’t even use language like “one true love” or something that would imply it’s something you have no control over—it’s just the one person that they happen to love more than anyone else, at that particular moment. Mind-control, or even simple abuse and torture, can get someone in “the right frame of mind,” so to speak. I mean, this very same book has a spell called mind rape and yeah, that will do it. So will the far more benign-sounding (but no less terrifying) programmed amnesia in Complete Arcane and Spell Compendium. Non-magical means are also plausible, albeit perhaps even more awful. For instance, the spell only cares about who they love the most, so if you take away everyone else they love.... And the spell explicitly states that someone not having anyone they love most is extremely rare, so apparently dead loved ones don’t count.
Sure, that takes a bit of set-up time—but you have time. You can literally do this anywhere in the multiverse, without interacting with your subject in any way. There is no reason why they should have any clue it’s coming. And if you have enough 5th-level prepared-spellcaster minions, that 2d6 damage each can be multiplied any number you like. Having a mass of low-level minions is rarely useful in 3.5e, because they just all die, but here it certainly is.
So yeah, love’s pain. It’s a terrifying thing. Overkill for a lot of stuff, but at a certain point, a sufficiently-paranoid, high-enough-level spellcaster becomes literally impossible to seriously threaten by almost anything. A lot of the time, love’s pain is going to be one of the very, very few exceptions available. The only protections are constantly staying in an antimagic field or dead magic zone (and if you can force someone to do that, you’ve as good as killed them for most purposes), or to be literally immune to death-by-damage (which is, preposterously, possible).
Hey I Can Chan points out familial geas, an 8th-level (6th-level for bards) compulsion from Heroes of Horror that works like geas except if you die without completing it, your closest adult relation gets the geas instead (but gets a chance to save and end the effect). No damage redirection, but it’s probably the only spell in the game that cares about familial relations.
As for actual damage redirection, pretty much everything is local, cast on the one you’re redirecting damage to or from, and has nothing to do with the relationship involved. The caster is basically always the “other” involved in the equation as well: you can redirect damage from an ally to you (e.g. shield other, found on many spell lists), you can very occasionally redirect damage to you to an enemy (e.g. the shield self ability that a binder can get from a pact with the vestige Dahlver-Nar), and those are pretty much the only options available.