I can guess, but have no statistical info on which types of sex offenders would be most likely to escalate to the murder of an entire family. If anyone does, I'm all ears.
I'm also only guessing, but it seems like all of them would be somewhat more likely to commit sex crimes than the general population. I'm thinking that the ones registered for violent offenses would be significantly more likely to murder a family than flashers. Many child molesters are not violent they are perverts who take advantage of children. My opinion is that any person with a record of violent crime would be more likely to murder a family than the general population. I would further speculate that a person willing to murder a family of three already has violent criminal record.