REGARDING SHINRA ELECTRIC COMPANY AND RUFUS SHINRA
While ShinRa Electric Company is a moderately small business in the muggle world, it is a huge deal in the wizarding world. The company itself is involved in both "good" sides and "bad." However, it is fair to say that the company is neutral, only working for its own benefit.
Rufus, personally, has the equivalent education of a graduate school student in economics and law; he is somewhat more geared towards the political aspects of business. Thus, while his father was still in charge of the company, Rufus was the wizarding world envoy and played politics harshly until Dumbledore pursuaded him to attend Hogwarts to develop divination.
He doesn't really attend Hogwarts as a school, more like a part-time university student. Currently, he's supplying modified mako to both sides (Dark and Light) and is negociating terms of payment.
He thinks his mother is Jenova, though his memories are actually of his father's wife. Rufus's father, who got his muggle wife pregnant, wanted a powerful wizard son and nothing less. He didn't risk Ansem or Voldemort's followers, wanted someone for ShinRa and not one of the Dark Lords, and instead Russia's answer: Jenova. He sought her out, since she was extremely well-known, and paid her millions for her DNA. His company performed a very advanced egg-splitting surgery to have her DNA injected into his child.
That child was Rufus. The muggle who gave birth to him was very sickly through Rufus's childhood and eventually died, but she is the "mom" that Rufus remembers physically. Rufus, however, visited Jenova's grave afterward, so he believes that she is his mother.
REGARDING JENOVA
During Dark Times, Russia lapsed into fear over a witch not quite as powerful as Voldemort himself, but one who was seen as the large country's substitute for him, per se. Although Her surname was never known, Her first name was known by just about every single Russian at that time -- Jenova.
She terrorized the people of Russia for some time, who became afraid of Her, infamous in Her own way. However, when the Dark Lord fell, She slunk away into hiding, and no one ever heard of Her again. Instead of flaunting Her powers and skills and using them for darkness and evil, She hid away in a dank little town in western Russia with her three sons, Loz, Yazoo and Kadaj.
However, the dark witch and wizard hunt was on, and anyone who had been reasonably close to Voldemort or been one of his followers was hunted down vicisously, and Jenova, fearing for Her sons, faked her own death and stowed away to England, taking an assumed name -- Anastacia Svetlonov -- and began a new life in one of the richer parts of London, waiting for Her time to rise once more into power. When she fled Russia, she left a "coffin" of sorts where her body was supposed to reside.
Fearing Her sons would forsake Her, and wanting to keep them close rather than let them wander and stray, She put a cruel and insanely strong hex on each of them, somewhat hypnotizing them into strict and endless loyalty to Her, turning them almost into puppets. Her favourite and youngest son, Kadaj, She allowed the ability to speak to Her through his mind... keeping a link to him so She could keep an eye on them all.
All three of her boys were eventually sent to Hogwarts, where they began their schooling, keeping in contact with their Mother through owls and the voices in Kadaj's head.
REGARDING GEOSTIGMA
There are two types of Geostigma.
Geostigma itself is a derivative of mako energy made for the consumption of humans in constant medical pain (i.e. chemotherapy patients). ShinRa produces it and sells it for a high price. Legal Geostigma is like morphine or Vicodin supplied to hospitals and is a purely wizarding drug. Most people don't recognize it by name and associate the term with the other kind.
Jenova creates this "other" kind, which is generally called by the name "Geostigma." Jenova created this herself and produces it at her own will, generally on the black market. It is illegal, because its effects on people who consume it vary dangerously. One thing is certain, though. Consumers of this drug are known to hear Jenova's voice, as if they've opened a temporary channel to her. Jenova distributes it to her children in order to gain more followers at Hogwarts. It is known that consumers become her followers, and many begin to call her "Mother."
At Hogwarts, Geostigma can be acquired from one of Jenova's sons.