So I think the key to a personal story is starting with the backgrounds your players gave you for their PCs. I started with my own idea of an epic story that would be very much about the players and would also tie into the video games (something that's important to me, but might not be to you).
My base story was that this group would be responsible for the Blight. In the books and games, we learn that actually it was The Architect who was responsible. He tried to infuse Urthemiel with Grey Warden Blood (a process that creates intelligent darkspawn like himself) and "something went wrong" waking the archdemon early. In my story, four very powerful Rage Demons have decided that The Architect's plan will ruin their fun. If he successfully merges the darkspawn and human societies, everyone will essentially be darkspawn-like and will no longer dream, making it impossible for Demons to posses them or watch them or anything. So these demons have infused the players with power in order to get them to stop the architect. The players don't know this of course. They only know that something has granted them powers and has been leading them in the direction of stopping the Architect. Stopping him from what? All they know now is that he wants to "bring peace" which doesn't seem that bad, does it? Ultimately the players will learn everything and have to decide the fate of the world. Help the Architect and stop the blight, but doom humanity to becoming more like darkspawn, or help the demons and secretly corrupt the Architect's experiments, causing the blight and bringing about the deaths of thousands.
For fun (and profit), the players occasionally have experiences in the Fade where the demons give them visions of how horrible things would be if the Architect succeeds. While they are "out" the demons are actually possessing them, running around Ferelden doing HORRIBLE things with their bodies. The first time, this lasted a week, the second time THREE MONTHS. The players remember nothing of what happened and only know that for some reason the Chantry and Templars are after them.
That's the long-term campaign story. But of course I wanted to also tie in the characters' specific backgrounds. Here's what I got from them:
Imekari: half-qunari, half-avvar, raised by avvar, abandoned by father, wants to find him
Elden: apostate mage, very superstitious, lost his best friend in some accident that Elden blames himself for
Godric: templar in training, has a younger brother that he hasn't seen in forever
Reza: City elf, stuck in a marriage he didn't want, fled to find adventure
Ashana: human raised by elves from a very young age, considers herself an elf in every way
From all this I created a single human antagonist for the party to chase while they're trying to figure out what's up with these powers and dreams and missing memories. He is a slave trader named Atilio.
Imekari: is actually fully qunari, was traded to the Avvar in exchange for helping Atilio escape Ferelden to Orlais
Elden & Godric: Elden's friend and Godric's brother are the same man, murdered by Atilio when he stayed behind to let Elden escape (they had seen Atilio transporting slaves and he wanted no witnesses)
Reza: Reza returned home to visit his parents only to find that his estranged wife had teamed up with some slaver (Atilio) and kidnapped many of the elven children. Many of the adults (including Reza's parents) went after him and haven't been seen since
Ashana: Atilio is actually her father. The elves stole her from him because he had stolen their children.
All this stuff came out in pieces over the course of a year of playing. They have only just recently put it all together and are now actively perusing Atilio. Of course it won't all be cut and dry. It still has to be a hard choice. I came up with a new (actually very old) race of humanoids called the Taltos. They are lovely people. Peaceful and kind. The party has actually met them. They should have died out centuries ago, but the lineage of one family has kept them alive, bringing them the only food their digestive system can tolerate. That lineage is the family of Atilio (and Ashana). That food is the elves that Atilio is not able to sell, mostly the old and/or otherwise feeble. What's that? The only thing the Taltos eat is elves that they get from Atilio? And Atilio may have kidnapped Reza's parents? And the party encountered the Taltos shortly after that and ATE THEIR FOOD? MUAHAHAHAHAHAH
Soooooooooooooo yeah. That's a really long post. Feel free to steal any of it, but I think the key to a dark personal story is to base it on your players' character concepts. Have all sorts of terrible things going on in the background that they slowly learn about, but also adapt. When you get to know their behavior, abuse it. Reza is a huge man-whore, so the Taltos ladies were very sexy, but because they are very fragile, mating with other species often results in their death. Reza finagled four of them into a fivesome and THEY ALL DIED. Elden really likes women who find his inane stories interesting, so one of the Taltos hung on his every word after he healed her. "You didn't use magic, did you?" "No of course not!" He assumed she just didn't like mages just like the most of the rest of Thedas, but oh no... When he got her pregnant with twins, the children inherited his magical powers. (Taltos grow VERY fast, btw.) A Taltos mage is a terrible thing. They killed their mother and were clearly mad. Elden had to lead the party in killing his own recently born children. Dark and personal enough?