In my training and in my work I have found say its not unheard of, or rare and is quite common for siblings and other family members to have the same dissociative disorders, same PTSD, same type of depression...

all it takes is family dynamics.

Most if not all child abusers is someone the child knows... family member, friend of the family, teacher...

Dissociation is one of t hose things that is perfectly natural thing to do for all kinds of reasons... stress, trauma, boredom, even medications can cause a person to dissociate..

Add to that extreme, long term abuse...

Add to that the family dynamics.. when there is abuse in the family there is an unspoken "code" you have the perpetrator / abuser, the caretaker(s), the scape goat(s), the perfect one(s),.... on down through the family unit..

most if not all child abusers that find their victims in families usually have a preference of age.. the starting point and the ending point where they are drawn to their victims. an abuser has their "thing" that draws them to abusing. sort of a mode of operation, signature, what turns them on. just like say a person that commits some other crime. there is something about committing that crime that makes the perps body produce their thrill, high. actually not unlike someone who for example has an eating disorder, addiction, or self injury. perps have their rituals (patterns and ways of abusing)

put it all together you have the makings of multiple family members having the same mental disorder..

example we just transferred a case of three boys from the same family ages ranging from 8-17 for more long term treatment, all of which showed on a psychaitric evaluation to have dissociative disorders to various degrees including they all have DID.

yes DID has diagnostic criteria that is hard to meet But everyone with DID can have it to different degrees. one may have all the diagnostic criteria and have co consciousness, another can meet all the diagnostics and have no co consciousness and other can meet all the diagnostics and have a multitude of variances in how much co consciousness they have with each alter/part. look at all the people here that have DID. no two members have it the same way but all have it.

in this case a teacher recognized bruising and other tell tale markers of abuse, reported it and the children placed in protective custody.all were abused from the ages of three and ongoing. all three were abused by their father, these boys were in family dynamics terms the "scape goats." their father abused them all starting at age three. how he started and proceeded was the same (his mode of operation, his pattern of abusing his children) So all three boys underwent the same extreme abuse.

in our work at the crisis center we treat many family members that end up having the same dissociative problems, same PTSD problems and same Depression problems when ever the abuser is a family member. our statistics show that a majority of our clients where we are working with more than one victim in the family theres a high rate for family members having the same problems. like any other problem in family units dissociative disorders is like they say in AA about having an alcoholic in the family.. its not just the alcoholics problem its the whole families problem too because it affects the whole family.

how does it work with multiple family members having DID and alters interacting.. it works the same way as having only one member of the family with DID and their alters interact with family members. DID is a trauma / trigger related disorder. the person with the disorder encounters something they cant handle, they dissociate and their alters take over control.

as far as I know through my training, work and having DID alters interacting with family members regardless of how many family members have DID it isnt a case where the family member chooses to dissociate so little Jan inside big Jan can play with little Greg who resides inside big greg.

Also the diagnostic criteria is that which says the alters "take" control. the diagnostic criteria also says in children the alters cant be there to be invisable friends or other fantasy play.

you can find the diagnostic criteria here http://www.behavenet.com/capsules/disorders/did.htm