Personality disorders are not per se genetically linked in family members. It is possible that individuals had learned poor social/coping skills from one another. True personality disorders are also not per se cured but if an individual diagnosed with one is willing to see professional help, that individual may learn some healthy coping skills to manage the symptoms of their disorder.
Some individuals may have these traits without having a true personality disorder
"Lack of insight, callousness, overspending, self absoption, no empathy" If a child had not been exposed to learning proper moral/coping skills this is not unusual. Initially children learn through the modeling they receive from adults/parents/caretakers (social learning)
In regard to the causes of autism there is still a lot of controversy out there. One of the possible causes is genetic in nature and yes you're correct this can be evident in siblings/twins. Immune deficiency is a speculation as well as vaccination as possible causes. Research at least proves that people with autism process information differently than those without the disorder.
My personal belief is that both biological and psychosocial factors shape a person's adult behavior and may predispose to different mental health disorders.