How Is Ambrose Related to Sabrina on Netflix’s ‘The Chilling Adventures of Sabrina’?

One question that has been bothering fans since The Chilling Adventures of Sabrina debuted is Ambrose’s back story. Now that the Christmas special, A Midwinter’s Tale, has premiered, fans are still wondering just how Ambrose is related to Sabrina. Here’s what we know so far. (This post, of course, will have spoilers for Season 1. It will not contain comic spoilers.)
Ambrose refers to Sabrina as “cousin” and he calls her aunts his aunts too. But it seems that they aren’t directly his aunts, since so far we only know about one brother that they have — Sabrina’s dad. So how Ambrose is related to Sabrina is still a mystery. It’s likely that he’s more of a distant relative and calls her “cousin” out of convenience. Here’s what’s been revealed in the series so far about his background. (Note: His exact relation to Sabrina has been spelled out in the comics and in the previous Sabrina TV show, but it’s unclear how closely this series will follow any of that, so this story will only discuss what has been revealed in the current series, along with non-spoiler fan theories.)
We learn in Episode 8 that Ambrose — who is much, much older than he looks — has a fascinating background and he’s very intelligent. He went to Oxford, published poetry at the age of 17, taught stage magic to Houdini, and painted with surrealists. Father Blackwood shares all of this when he and Ambrose have a heart-to-heart, before he agrees to extend Ambrose’s house arrest so he can go to the Academy of Unseen Arts and work with Father Blackwood. 
We learn that Ambrose was involved in a plot to blow up the Vatican, after he found a father figure in a man named Crowley, who was devoted to the Dark Lord. (In real life, Aleister Crowley was an English occultist who founded a religion called Thelema in 1904 and identified himself as a prophet. It’s unclear if this is supposed to be the same Crowley that Ambrose followed.)
Ambrose’s own father was killed by witch hunters when Ambrose was very young. It’s possible that his father is the Spellman who connects Ambrose to Sabrina and her aunts, but this isn’t explained.
After he plotted to blow up the Vatican, Ambrose refused to take immunity in exchange for giving up his co-conspirators. He’s been under house arrest for about 75 years, which makes him much older than he appears.
Fans have a number of theories about Ambrose, but one theory can be dispelled simply by knowing how long he was under house arrest. Some fans think there is a connection between Sabrina’s parents dying in a plane crash on the way to the Vatican and Ambrose planning to blow up the Vatican. But Ambrose’s crime happened about 75 years ago, while Sabrina’s dad died about 15 years ago. The two incidents were separated by about 50 years.
Other fans think that Zelda and Hilda have at least one other sibling who simply hasn’t been named in the show yet, and that person would be Ambrose’s parent. Remember, all the witches are much older than they appear because they all age very slowly.
How do you think Ambrose is related to Sabrina? Let us know in the comments below.