Some of the most recent heinous murderers have had family present during hearings and trials.....
Casey Anthony, Scott Peterson, Chris Watts, Christian Rivera Mollie Tibbetts killer, the list goes on and on.
I even saw a recent interview type show with John Wayne Gacy's sister. I started watching so angry and predetermined in my mind to not really like her, to judge her, and to blame her for his actions. They would have to have known right!
By the end of the show, I had some compassion for the sister. Her quote was "I loved John as a brother, not as a murderer".
I guess my point here being, I loathe these killers as much or more than anyone, especially JP. I've never been so invested in a case as with Jayme. She touched a part of my heart and soul with her innocence and then with her strength and courage as she escaped. She gave many people a renewed Hope in general.
That said, IMO, JP's family legally has a right to be present in court. They have reached out to the Closs family and expressed sympathy. Okay once, twice pushing it. Now, attend out of love for your son, brother, etc. if you feel so inclined, but please keep the Closs name out of your mouths going forward. This is about justice for Jayme and her family, period.
JMO
You are speaking in the first part of your post about people who are not sociopathic
serial killers who would likely kill again and again if they were released from prison if still living. ( Gacy, the person you go on to talk about, was a sociopathic serial killer who died in 1974).
The definition of a serial killer is a person who has deliberately and without provocation killed at least 2 people not related to him/ her and if not stopped, would likely keep on killing for therein lies the thrill.
The family member who could possibly be his victims are either the killer's first victims or he never goes back to the family as he's separated his current life from his past life except for maybe one fixation on a person who becomes the prototype for his victims, overwhelmingly complete strangers to the killer who likely share some physical traits ( gender, age, hair length or color or both, ethnicity) the killer was looking for.
Historically, a very few serial killers did have such a fixation on their mother, who likely also had a very obvious pathologically unhealthy need or control to some extent over the killer. This is not found in modern times, but when we were first learning about serial killers, we did find that some would have either a symbiotic attachment to their mother, or a reaction formation which manifested as looking like an attachment until the pathology of the killer evolved and he killed his mother, too.
The reason we do not see SKs hanging out at mommy's house is likely due to the easier ability in modern decades to travel long distances, to live on the streets or in the woods with the multitude of homeless people who are not serial killers, thus avoiding being arrested for a loitering charge, and to easily relocate to a different part of the country through our extremely improved network of corridor highways.
IMO, the overwhelming change is the mobility afforded by our extensive building of superhighways.
The killing at will of complete strangers is a deviant act and a compulsion which cannot be stopped by either the killer or society, not that any serial killers have actually ever wanted to stop killing- it is their reason for living. All we have to keep them from killing more people is to lock them up for life, or put them to death in states with the death penalty. They lost all moral values early in their lives, sometimes as children, usually as teens through a process we still do not completely understand ( or we likely could cure a budding sociopath)
J. Patterson, is, in my opinion, a sociopathic serial killer. He killed 2 innocent strangers in wanton disregard for their lives and likely would have killed their daughter had she not escaped.
All the people on your list,now that I look at it, killed a family member or members except Mollie's killer. Because of the relationships which existed,
they were not killers who stalked a particular type of child, or adult and kills them and others, with the killings usually fitting into a pattern of behaviors.
Thus, they are not serial killers but are bad people, of course. I would never ask any of them ' Why did you do this?" because I don't care why they did it, I care that they did it.
John Wayne Gacy
AND his sisters endured extreme abuse in their childhood home together at the hands of their father. He was a violent alcoholic and while John was said to have a heart problem and was a " Mama's boy" , it's likely his sister or both sisters were treated just as badly as he was if not worse.
Therefore, it's likely the sister who came to his trial had her own psychological traumas related to their shared childhoods and could not separate HER childhood and likely, shared protection when John's pathological need to kill was being formed. John Gacy was absolutely a sociopathic serial killer.
His sister's life was likely not enhanced by any part of his trial, and he would not have cared if a busload of relatives showed up for his trials.
When we look at behaviors, we look at the cause and effect, and the payoff for each person. The cause of his sister likely attending his trials has already been discussed- a childhood bond due to their father's brutality. The payoff for attending was possibly a feeling that she'd " supported" him, but no, she didn't. The effect of her being there was ZERO. She was nothing to him. Absolutely nothing as in a blank piece of paper being blown in a vacant parking lot. I know this because it is the core lack of the ability to feel love or remorse, or pity or even fear that sets the sociopath apart from the rest of society and allows him to kill with reckless abandon.
Therefore, her presence was likely very harmful to her, because the evidence had to be brutally graphic, and her presence was absolutely a matter of total indifference to Gacy, as the sociopath cannot respond to positive emotions by others. They can use the other person or people as a means to their own end of either killing, period.
Her presence was her choice but it was a choice tied up in memories of him as a child, not the understanding that he stopped having ( or never had) any positive responses to her or any other person in his life, except maybe his mother, which is a feature of serial killers.
She missed or grieved for a child she loved, but that childlike behavior disintegrated into sadistic killing early in his life and it's likely she never saw him in his adult killing years. Thus, a true family relationship did NOT exist except in her memories in her mind. It was not the reality of the situation.
I have pity for the innocent families who likely do not understand what monstrous thoughts and actions arise out of the killer's psyche and cannot be stopped except incarceration for the remainder of the killer's life, because some people lack the ability to look at the person as they actually are, not as a family member remembers them in childhood.
I still believe that attempts by a family member to connect with a sociopathic killer who's been caught and is facing trial or has been sentenced and is incarcerated for life ( or put to death in states which have and use the DP) are both futile and likely, emotionally hurtful for anyone who tries ( those who cannot be used by the sociopathic killer from prison for any reason. We know that some serial killers have misused superficial attempts to connect with them from their prisons). If the woman who writes to the Ted Bundys in the world truly understood what that man would do to her if he had her alone for 10 minutes, no letters or cards would be sent unless she's seriously mentally ill or otherwise lacks the ability to make rational decisions using even basic judgment.
I agree having to have Jayme testify would be horrible and traumatic, but if it put the murderer of her dearly loved parents behind bars for LWOP, I believe she'd rise up again and be able to stand for them. 
