If you pay attention to the background when Cal uses his Force powers to save Prauf on Bracca, there is a probe droid watching the entire thing. This means the Second Sister knew exactly who Cal was when she threatened to sacrifice the other workers unless the Jedi she was searching for exposed himself. In other words, it was a test: if he stays quiet and sacrifices everyone else, it would have meant he was already on the path to the Dark Side and they could capture and turn him. If he exposed himself, they still win because it would be one more dead Jedi they no longer had to worry about.
There's more layers to it. The Empire knows he gave up his identity to save Prauf, they have the footage. So they're testing his loyalty to his friends, and his friend's loyalty to him. There's only a few outcomes the Empire would expect out of this, given that they know Cal won't give up his friend, even for the sake of his identity.
Prauf turns in Cal, the betrayal being something the Empire can use to force his turn to the dark side.
Cal gives himself up to save Prauf, and the Empire can kill them or torture Prauf to get Cal to turn to the dark side.
Cal tries to run away with Prauf, who definitely can't keep up, and the Empire does the same thing as above.
None of these outcomes are good. But Cal still survives, with his soul intact, despite there being nothing he can do to come out of this without being heavily pushed to the dark side. Why? Because Prauf beats the test. He takes the fourth option, where he starts saying things so treasonous that the Empire has to kill him or look weak. When he's dead, he can't be used against Cal as either a hostage or a liability when Kestis inevitably has to run. Prauf took what the Empire thought was a Xanatos Gambit and destroyed it.
The reason the Empire didn't think of this? The one thing the Empire doesn't understand: Friendship. Prauf cared more for his friend, who saved his life, than he did about surviving. Some random nobody giving up their life before giving up their friend is unimaginable to the Empire, so they never planned for it, and just killed Prauf for being uppity, not realizing that he was the only thing keeping Cal from taking off.
Of note is that this op, and Prauf's death, were both done by Second Sister, who we learn has a pathological distrust of undying loyalty because Cere, her own master, gave her up to the Empire.
Cal's arc is all about him learning to trust again, including the Force, his companions, and finally himself. So naturally when Greez and Cere first rescue him, he spends a few moments aimlessly standing in the cockpit holding his light saber up in a guard position, which Greez points out is really dangerous. He's not thinking clearly; he's in a confined space surrounded by strangers in full-blown Fight or Flight mode because he barely has any reason to trust these people, beyond the fact that the only other option is facing off against the Inquisitors.
Cal defeats Trilla with a surprising amount of ease in their third duel, likely due to the latter's overconfidence. The Second Sister was no doubt expecting Cal to be the same frightened Padawan who narrowly escaped death in their previous encounters. However, by that point in the game Cal had already successfully fought the Ninth Sister and Taron Malicos, both of whom were former Jedi. So although he was still technically a Padawan, his skill level was already on par with a Jedi's, something that Trilla was not prepared for in their third encounter.
There's also the subtext that Trilla subconsciously didn't want to win. She didn't kill Cal when he was hit with a Heroic BSoD by the overwhelming psychometry backlash of holding an Inquisitor's lightsaber, even though she could have; she kept the Holocron on her person during the final duel, even making sure he knew where it was, when she could have locked it up. She was visibly on the edge of turning when she was killed. Her response to Cal's insistence that he won't let anyone hurt the children once he's found them ("I said the same thing, once") does not speak to any real conviction in stealing the next generation of Jedi for the Inquisition. She didn't want the Empire to get that holocron, not really.
Trilla knows what it feels like to have Force-sensitive children ripped from your arms and subjected to Imperial torture. Cal was fighting to keep that from happening. Of course a part of her wanted to help him.
Cal's relative ease in wielding a double-bladed lightsaber after being disconnected to the force for a couple years can be explained by his Psychometry. Remember that the lightsaber Cal wielded belonged to his former master Jaro Tapal, who utilized a double-bladed lightsaber style: the Jedi Master's memories, skills and techniques slowly bled into his Padawan the more Cal wielded Tapal's weapon and re-established his connection to the force. Not to mention those times whenever Cal has a flashback to his master's training sessions may actually be a bi-product of his Psychometry with his master's saber rather than his own memories. This may come to a full circle by the time Cal faces off against Trilla for the last two encounters, as rather than fighting a Padawan, she was actually fighting against the likeness of Jaro Tapal instead!
Cal's skill in psychometry actually serves as plausible justification for some of the more out-there things he does, like hijacking an AT-AT or opening Force-imbued objects he's never laid eyes upon, or never had the clearance to access in the first place. He's drawing upon the memories and skills of those who used the things he now uses to make getting the hang of them much easier.
The Second Sister was explicitly a Padawan, so why is she ranked so highly even against the one Inquisitor whose rank we knew before (the tenth). The Dark Side draws on anger and rage, and her backstory provides an ocean of it to draw on.
Outside of The Grand Inquisitor, there were no ranks between Inquisitors. However, there still is an unspoken hierarchy. In the comics, Vader would duel and maim those he felt were sticking too much to their Jedi roots. Yet the Second Sister was still "whole," compared to Nine missing an eye and a leg. Why is that? Because not only was her Jedi training incomplete and thus easier to mold, but her trust in the Jedi being shaken that hard probably made her a whole lot more powerful in the Dark Side.
During Attack of the Clones Obi-Wan tells Anakin “Your weapon is your life.” when handing back his lightsaber. When Cal grabs Trilla’s lightsaber he sees the life she’s lived since the Empire got her. It’s also poetic as he gives it to Cere, meaning Trilla’s life was in her hands.
Although his training with Tapal wasn't finished, Bracca was a great place for Cal to end up. The opening of the game shows that the average day is chock-full of running, jumping, climbing and acrobatics. Scrapping also helps with focus, physical control and observation, and gives him a grounding in mechanics.
Why does Jaro Tapal wield a double-bladed lightsaber? Because the main weapon of a Lasat is a Bo-rifle, which is a staff with an electromagnetic tips on each end, a Double Weapon like Jaro's lightsaber. Jaro May have chosen the double-bladed lightsaber because it's the closest thing to a Bo-rifle the Jedi Order has.
Cal's Psychometry allows him to feel the memories or feeling of the last people who held objects he touches. Keep in mind that he worked on Bracca for five years, cutting and dismantling ships that were destroyed during The Clone Wars, and that as such they were probably full of fear and despair that he felt every day. It's a wonder Cal didn't fall to eh Dark Side from all of this.
There's a good chance that many of the Republic-aligned ships, weapons and armor Cal has been scrapping for the last several years were part of the same fleet he served in during the war, which means that he'd be reliving the memories of the troops that killed his master. It's bad enough that Cal saw Jaro die before his very eyes, but one shudders to imagine the kind of nightmares he'd have if he touched a discarded clone's rifle and experienced the horror that is having your body stolen out from under you and being forced to kill your leader and the apprentice you treated like a little brother, all because some maniac in a cloak you've never seen before said three little words: Execute Order 66.
Nearly every Jedi Cal meets in the game has either fallen to the Dark Side or struggled against its pull in the wake of Order 66. This implies that the isolation and fear felt by many Jedi survivors made it difficult to resist turning to the Dark Side. Being constantly hunted by the Inquisition no doubt made things even worse, as they were more than willing to mold any wavering Jedi into one of their own.
