The original Charmed Ones were three sisters who happened to be witches.
In 1998, Penny Halliwell, the grandmother of the Charmed Ones, died of a heart attack. This led to the Charmed Ones acquiring their powers not long afterwards (Patty Halliwell having been murdered by a Water Demon some twenty years previously).
NAME: Prudence Halliwell
DOB: October 28th, 1970.
OCCUPATION: Former Museum employee, former Auction House employee, former photographer.
KNOWN POWERS: Telekinesis, astral projection.
KNOWN RELATIVES: Victor Bennett (father), Patricia Halliwell (mother, deceased), Penelope Halliwell (grandmother, deceased), Piper and Phoebe Halliwell (sisters), Paige Matthews (half-sister), Leo Wyatt (brother-in-law), Wyatt and Chris Halliwell (nephews).
Of the original Charmed Ones, was Prudence Halliwell who would have the most contact with Rex and Hannah. Indeed it was she whom Rex and Hannah had initial contact with. In 1998, shortly after the Charmed Ones first acquired their powers, Rex, called Prue and offered her a job at Buckland Auction House. This was, of course, a ruse to keep Prue, and her sisters, under observation.
Although Prue got along well with Rex, with Hannah, however, there was friction. Of course, Prue was unaware of Hannah's true intentions, rather she just thought that Hannah saw her as a rival. On one occasion, due to a truth spell that Prue had cast, Hannah blurted out: “It’s my mission in life to destroy you.” At the time, Prue didn't realize that Hannah was speaking literally.
It was Prue that Rex tricked into releasing Matthew Tate from the locket that her ancestor, Melinda Warren, had trapped him in, back in the 17th Century. The plan called for Matthew to acquire the powers of the Charmed Ones and deliver them to Rex and Hannah. However, due to Matthew's overconfidence, the plan failed.
Finally, in early 1999, Rex manipulated the situation in which Prue found herself accused of the murder of Jaime Lopez, a security guard at the Auction House. Rex then offered the sisters a deal, give him their powers, and he would help clear Prue of the murder charge. Having no other option, the sisters relinquished their powers, which flowed into a lantern that Rex had provided for them. However, Rex then tried to kill them, having been ordered to do so by the Source. Hannah, having turned into a black panther, charged the sisters, but the intervention of Leo Wyatt saved them. The Halliwell regained their powers at the last second and used them against Rex and Hannah, defeating them. Rex and Hannah were then recalled by the Source.
Prue Halliwell would go on to have many more adventures with her sisters, until she was killed by the Source's assassin, Shax, in 2001
In 2008, when Rex and Hannah returned to San Francisco, following the Warlock Revolution, they encountered the ghost of Prue (along with those of Patty and Penny Halliwell), who informed the two former Warlocks that they would be encountering the Charmed Ones before long. Indeed, said meeting did take place not long after Prue's prediction.
As of this writing, there has been no further contact between Rex and Hannah and Prue Halliwell.
NAME: Piper Halliwell
DOB: June 7th, 1973.
OCCUPATION: Former chef, now nightclub owner.
KNOWN POWERS: Freezing time, exploding things.
KNOWN RELATIVES: Victor Bennett (father), Patricia Halliwell (mother, deceased), Penelope Halliwell (grandmother, deceased), Prue Halliwell (sister, deceased) Phoebe Halliwell (sister), Paige Matthews (half-sister), Leo Wyatt (husband), Wyatt and Chris Halliwell (sons).
Unlike Prue, Piper had no direct contact with Rex and Hannah until the final battle between them and the Charmed Ones in 1999. It was Piper's boyfriend, Leo Wyatt, who saved the sisters, using his white lighter powers (although Piper was unaware of Leo being a white lighter at this time). Piper would eventually marry Leo, two years later, and they would have two sons, Wyatt and Chris.
Upon Prue's death in 2001, Piper and Phoebe would meet their half-sister, Paige Matthews.
When Rex and Hannah returned to San Francisco in 2008, Piper, Phoebe, and Paige soon encountered them. In the end, Piper and her sisters reconciled their differences with Rex and Hannah, and the former enemies became allies. Rex and Hannah ended up becoming the God uncle and aunt to Wyatt and Chris.
NAME: Phoebe Halliwell
DOB: November 2, 1975.
OCCUPATION: Advice columnist.
KNOWN POWERS: Premonitions, levitation, empathy (although the latter two powers were taken from her, and it is not known when or if she ever regained them).
KNOWN RELATIVES: Victor Bennett (father), Patricia Halliwell (mother, deceased), Penelope Halliwell (grandmother, deceased), Prue Halliwell (sister, deceased) Piper Halliwell (sister), Paige Matthews (half-sister), Leo Wyatt (brother-in-law), Wyatt and Chris Halliwell (nephews), Cole Turner (ex-husband), Coop (husband), Children (names unknown).
Like Piper, Phoebe would have no real contact with Rex and Hannah until the final battle. As part of Rex's plan to frame Prue, he began dating Phoebe. However, it was all a ruse, as Rex's heart belonged to Hannah.
Phoebe was present in 1999, when Rex and Hannah were defeated.
Phoebe would have many more adventures in the years to come, even becoming romantically involved with the human/Demon hybrid, Cole Turner.
Upon Prue's death in 2001, Phoebe and Piper would meet their half-sister, Paige Matthews.
Phoebe ended up marrying a cupid named Coop, whom she would eventually have several children with.
It was Phoebe who first encountered Rex, in 2008, following his and Hannah's return to San Francisco in 2008. This led to the encounter between the Charmed Ones and Rex and Hannah soon after. In the end, Phoebe and her sisters reconciled their differences with Rex and Hannah, and the former enemies became allies.
The Charmed Ones maintained contact with Rex and Hannah for years afterwards. They continued to keep in touch with the two former Warlocks following Rex and Hannah's departure for Arkham, Massachusetts, in early 2015.
After Joseph Philips tried to kill Hannah, the Charmed Ones visited her in Arkham Community Hospital and signed her casts (both of Hannah's legs had been broken in the attempt on her life).
Contact between the Charmed Ones and Rex and Hannah will no doubt continue.
Charmed Episode No. 2: I’ve Got You Under My Skin
Charmed Episode No. 9: The Witch Is Back
Charmed Episode No. 10: Wicca Envy
Rex and Hannah Chronicles Story No. 4: Revelations
Rex and Hannah Chronicles Story No. 34: New Frontiers
Rex and Hannah Chronicles Story No. 39: The Inner Circle