I'm sure there is a better and more official list than this, but here is my quick take on the characters:
LVD - Lori Vallow Daybell
CD - Chad Daybell
JJ - Lori and Charles Vallow's adopted son, JJ Vallow. JJ is the biological son of Charles' nephew and is the biological grandchild of Kay Woodcock (KW).
TR - Tylee Ryan. Lori and joseph Ryan's (Lori's 3rd husband) daughter. Charles Vallow's stepdaughter.
TD - Tammy Daybell. Chad's deceased wife. Allegedly murdered by Chad and Lori.
SG - Samantha Gwilliam. Tammy's sister. (Told LE about pet cemetery on Chad's property.)
Chad and Tammy's children are: Garth Daybell, Emma Murray, Seth Daybell, Leah Murphy and Mark Daybell.
CV - Charles Vallow (Lori's 4th husband). Children are Cole, Zach and JJ. (JJ is adopted)
KW - Kay Woodcock. JJ's grandmother and Charles Vallow's sister. Filed request for welfare check for JJ.
LW - Larry Woodcock. Kay's husband.
AC - Alex Cox. Lori's brother. Shot Charles Vallow. Alleged killer of Tylee and JJ. Died of apparent heart issue Dec 2019.
ZP - Zulema Pastenes. Married Alex Cox 2 weeks before he died. Part of Lori and Chad's group. Testified.
JC - Janis Cox. Lori's mother.
BC - Barry Cox. Lori's father.
SS - Susan Cox Shiflet. Lori's sister.
Adam Cox - Lori's brother. (don't know if initials are used since they match his brother Alex's.)
ZC - Zac Cox. Adam Cox's son. Lori's nephew who lived with her and Charles for a period of time.
MP/MB/MBP - Melani Boudreaux Pawlowski. Lori's niece.
BB - Brandon Boudreaux. Melani's ex-husband. Someone attempted to kill him. Testified at trial.
IP - Ian Pawlowski. Melani's current husband.
MG - Melanie Gibb. Lori's ex-close friend. Testified.
JR - Joseph Ryan - 3rd husband. Father of Tylee Ryan.
CR - Colby Ryan - son of Lori and her 2nd husband. Half-brother of Tylee.
I hope this helps!
And here is a link to a "who's who in the Daybell case" from East Idaho News, providing more detail:
Who's who in the Daybell case - East Idaho News