- Relocating/expelling them is probably the easiest "remedy".
- Unfortunate accidents is probably the fallback option.
- The "love" option is to examine each of them in detail and do whatever you can to rescue them. That's hard, and probably impossible in some cases, but I assume the sense of achievement if you pull it off is worth a fair while as well.
So why are they unhappy, and what can you do to counter that? The easiest ones it to make sure they've got access to clothes, grab their trinkets (which may have you study their detailed preferences to make trinkets specifically for them if they're picky, and then have them haul those trinkets).
Lack of friends is harder, but it ought to be possible to subject them to intense treatment using the latest research with hand picked future friends.
Family can be treated with nuptial encouragement suites, assuming they're the marrying kind (and orientation is important for procreational purposes, but for key dorf stabilization, you're looking for a match, with dorflets as a potential bonus (or scourge, depending on your view).
If they freak out at the sight of corpses, take them off of burial hauling as a minimum, and refuse hauling as well as a maximum. Always keep your corpse stockpile out of view for everyone except those who have business hauling corpses.
Those who pine after crafting: give them private workshops set to only accept themselves (can be rotated between dorfs or shared depending on your settings) and the appropriate job (and ban them from the "production" workshops, e.g. by imposing a lowest skill level for usage).
Etc, etc. for all the other needs. For food preferences you'd need DFHack script help, as DF lies to you about preferences.