Bad guy Sans's

Dust's fiance is Blueberry
Cross's husband(/wife) is Dream
Nightmares boyfriend is Killer
Horrors boyfriend is Lust
Errors husband(/wife) is Ink

Samuel, Scrooge, and Dark are Nightmare and Killers kids
Lurro, Tacky, Desire, and Luxath are Horror and Lusts kids

Nightmare, killer, Lust, Horror and the kids all live in Nightmares mansion in Dreamtale. Dust and Cross used to live here until they moved in with their boyfriends. Error live here for less than a week befor he decided that he preferred to do his evil business alone.
Now all the bad Sans's(including error) are retired and living the rest of their lives with the ones they love.... That doesn't mean that they're nice or good or non murderous. It just means they're not looking for trouble any more. It tends to come to them.

But boardom is their worst enemy now.
Nightmare likes to stay in his non corrupt form, it attracts too much attention for obvious reasons.