Highly debatable. The story never intentionally highlights it, but the diclonii's violence towards others can be read as a response to the violence they've faced in life.
One if the main characters is strongly implied to have been repeatedly raped by her father. Her mother assaults her when she tells her about it. Neither are shown on screen.
yes, a character endures graphic abuse by family, and another character is shown to beat up a woman and a little girl. characters are also slapped a few times by their friends.
yes. several characters are used as test subjects and have to be restrained during them, or while being transferred across the facility. there is also a restraint scene before an SA attempt, but the SA itself never happens.
The experiments done on the Diclonius can only be described as such. Lucy also has a tendency to play with her victims, cutting off limbs one at a time.
i personally wouldn't call it DID, i would relate it more to a fugue state, but a main character gets brain damage, and it results in her having two different 'personalities' and amnesia between them. said character does however refer to the second personality as "the other one" being asleep when not present, so it could still be seen as such for sure.
It is heavily implied that a main character dies of Suicide by Police.
In the manga specifically there is a direct depiction of a diclonius committing suicide with a knife.
yes, more than one character has "flashbacks", moreso to explain plots and backstories, but these all mostly contain traumatic memories. 2 main characters in particular have suffered memory loss as a result of trauma and remembering them causes them obvious distress.
Sort of. One female character has a fascination towards female anatomy and grabs breasts, and another female character kisses a younger version of the previously mentioned character. It is shown lightly that these female characters care for each other.
Both of these characters die before the end of the series.
Two of the main characters are cousins and have romantic and sexual themes together, this is treated very nonchalantly as part of the culture, though the culture has changed considerably since the release.
yes, a character runs away and experiences homelessness with her dog due to abuse at home. it is shown that she has trouble getting food and is looked down upon for her homelessness. she is welcomed into a household eventually.
The anime finished before the manga, leaving an open ended story with loose ends. Read the manga for closure, I would consider the anime ending unhappy and unfulfilled.