The Rugrats really were a figment of Angelica's Demonic and Unimaginable imagination.
Chuckie died in 1997 along with his mother, that's why Chaz is a nervous wreck all the time.
Tommy was born in 2000, but he was a stillborn, that's why Stu is constantly in the basement making toys for the son who never had a chance to live.
The DeVilles had an abortion in 2001, Angelica couldn't figure whether it would be a boy or a girl thus creating the twins.
As for "All Grown Up" the teenage Angelica became addicted to various narcotics which further aggravated her Schizophrenia, bringing her back to her childhood and thus her creations she obsessed over, because of time lapse between the present and the last time she interacted with her creations, she made them older. Angelica was constantly taking hits of acid, so she would never have to live without her creations who were her only company. In a judgemental world, Angelica's mom actually died of a heroine overdose in 1982 just after Angelica was born, and Drew in his depression married a gold digging whore that Angelica idolized because she fooled herself into thinking it was her real mom but always had a concept of her mom, Cynthia, and took a barbie doll and made it after her mom's image, wearing an unwashed orange dress and having jacked up hair, which is why she was so attached to it. Later in life she followed in her mom's footsteps with drugs and everything, dying of overdose at age 15 when All Grown Up! was "cancelled".
The only rugrat not to be fictional however, was unborn Tommy's brother Dil, whom was born in 2002. However, Angelica didn't know the difference between Dil and her creations, although Dil didn't follow her commands. One day in 2005, after endless crying and a refusal to disappear like the others did when Angelica was angry with them, she hit him. Due to this, he sustained a brain hemorrhage, which resulted in a deformation. As he grew up, his damage only became more evident and by the time he was 11 in "All Grown Up!" he lived as an outcast, being ridiculed for his weirdness and retardation. The immense guilt over this is what led Angelica to her drug use and is what led Angelica to un-create the Rugrats briefly, until her experience with hallucinogenics.
On a trip to Paris to find love, Chaz married a woman named Kira (He was actually going to marry a different woman named Coco, but she just wanted him for his money.) who had a daughter named Kimi that was torn from her because she was a cocaine addict (Angelica imagined her from Kira's stories). He lost his mind after the death of his wife and was in denial that she was ever prostitute. Upon return to America, Chaz and Kira married and she got her greencard. It was actually a really happy and romantic story. Kira continually stuggled with addiction, but was relatively happy with her life and Chaz
Suzie was actually Angelica's only friend, who entertained the thought of Angelica's creations, for her sake. Angelica spent the last days of her life in the back of the school cafeteria, imagining friends around her and playing with the lives of her creations.