I have a lot of thoughts about these two ships that other people have articulated in much more eloquent ways but ill try to summarize it as best i can.
loooooooong long rambling under cut :p
I see Avebela having the fun potential to lead into a redemptive (yes redemptive) arc for Aveline. As it stands within the second game, she's a fantasy cop, and god knows i hate the "butch/masculine female character is a cop" shit so so much. But, working with whats there, exploring Aveline's issues with doing things without a clear set of instructions or rules to follow with the way Isabela is sorta the polar opposite is so fun to me. Obviously Aveline is a capable woman, and is able to shunt institutional rules when she feels she's serving a greater good, but she's still stuck on a very specific idea of what right and wrong look like, and enacting justice is done best through carceral and/or violent means. (I'm sorry but marrying a Templar fucked her up lol).
Isabela is a character I want to read more about, and dive more into her meta, cus she also has very strong conceptions of what's right and wrong, but she tries to distance herself emotionally from the impact of her actions, and the actions of the systems around her. Knowing her history, its totally understandable. She also seems to be someone who desperately wants strong bonds with people, but is too afraid to show her hand too much. and its that fun intersection between these two that I love to chew on. Aveline ALSO wants strong bonds with people, and seems to be at least some sort of romantic, even if her idea of romance looks a bit different from the norm. She's more willing to extend her arm out, even through the fumbles. I'm a little fuzzy on the events that happened in Kirkwall after 2 (i recall Sebastian wanted to invade in a war-table mission and you could back him or Aveline, and I think Kirkwall kinda fell to the blight in Veilguard? Honestly whatever canon I'm making for myself, I'm seriously condensing timelines.) Before Hawke's crew split up, I imagine Aveline and Isabela had started to get a lot closer, but still ultimately ended up parting ways by the end of the game. It was only after multiple issues in Kirkwall that harshly revealed a systemic failure of the guard, and a subsequent rescue mission by a daring pirate queen, which solidifies their relationship, Aveline leaves the city and becomes the kind of knight she said she wanted to be. (also a small side note in my canon, aveline is the tallest and most jacked of the Hawke crew. and I like the idea of Isabela and Aveline exchanging scarves)
Fenders has so so so much to cover but I simply don't have the smarts for it lol. Those two to me is like sticking two glue traps together. idk what to say that hasn't already been said to death, so forgive me for being redundant. These two have so much in common, and the reason they aren't on solid ground with each other, to me, is because they both see in each other aspects of their abusers and that makes me start gnawing the bed frame. Also, again, as smarter people have said, these two are people who are hopelessly devoted to those they truly care about, and a scenario where they start deeply caring for each other would make them a deadly duo. It would obviously take time and some healing before that, but that's where re-writes, and making my own canon come into play. I think Fenris, similar to Isabela, desperately wants companionship on a deep level, but he not only doesn't feel he can trust others, but also himself. Most of his known life up until DA2 has been completely out of his control, and one of the few times he was able to take agency for himself, it still ended with what felt like a loss of control (by way of killing the fog warriors).
Anders is obviously a hopeless romantic at heart, even through his mental health struggles. He does have some difficulty getting close to people as well, though I think he reaches out anyway because he just cannot help himself. I think, especially because of his situation with justice, he does hold hatred of himself on a fundamental level. He tries to hold a lot of pride for who he is as a mage, but again he feels like he's constantly trying to hold back a dangerous aspect of himself, and that cant be dealt with fully while hes in Kirkwall, because he is basically constantly being re-traumatized for years. I think I could make the argument Fenris is also being re-traumatized, aswell, to some degree (being in a former slave city with literal golden statues of slaves, and active slavers in operation around the city. Not to mention still being hounded by Danarius.) Frankly I think all the Hawke crew is just dealing with trauma after trauma constantly for 6 (?) years. It is interesting to me that Fenris' and Anders' approaches to their actively threatening triggers is similar but still fundamentally different. Its possible I've missed some aspect of their stories, so take these next takes with a grain of salt. I've seen someone describe Fenris and Anders as two people at different stages of the same journey. Fenris is only really just getting started on figuring out who he is out from under Danarius' shadow, but he's still in survival mode and survival for him for quite a while has been "use what's right in front of him while he can, face the threat, and cut and run if the need arises. Don't stay attached".
I imagine that's how Anders probably felt when he had attempted his first few escapes from the mage tower. I think he held that self interested attitude up until his time with the wardens, and justice. It was only after he really started mulling over, not just his situation, but the whole system that he started facing his problems from the standpoint of using whatever power he had to help other mages. I think Fenris would reach this conclusion at some point, but it wouldn't happen in Kirkwall. He was helping free slaves while he was there obviously, and that is good, but he was still coming at it as an individual matter, rather than a systemic one. I don't compare these two to be like "Fenris just wasn't as good a revolutionary as Anders" because, one, that's a flawed way to analyze these two, and two, Anders wasn't a perfect one either. Like i said, they're on the same path at different points. They both still have a lot to learn. I mean, to me, one of Anders' flaws is his lack of intersectionality, which I think only fuels the animosity he and Fenris have with each other (not to even mention Merrill). I'm not mentioning this to be like "why didn't they write Anders as a perfect textbook revolutionary figure?" Because having him be flawless would just be uninteresting. However, i think considering this writing with a more modern lens could lead to an interesting arc for him, and Fenris. Growing and learning and helping together blah blah blah.
As a slight aside, if it wasn't clear, I think Anders was justified in destroying the Chantry. It wasn't the cleanest solution that could ever had been thought of or anything, but it was literally a last resort after years of other more peaceful methods (and frankly, even if the writers fundamentally disagree with its validity in a lot of ways, the overall writing in how the Mage/Templar fight shook out ultimately vindicated his actions ¯_(ツ)_/¯). All this to say, Anders needed to do what he did, and I can see the rest of the Hawke crew feeling varying levels of resentment towards him for literally upending lives they were just starting to place roots into. Fundamentally, the problem is that everyone in Kirkwall with a decent heart who tries to plant roots in that city are doomed to be ripped out sooner or later, because the rot of the city and its institutions is just too deep. I think even if Anders fell off the map entirely before the events of the game, something else would have happened to cause fractures in their lives because the city is designed to grind you down.
Fenris would feel anger, betrayal, and resentment towards Anders after having to leave. It would take finding people who talk about how Anders helped them to smooth his feelings out. And not just help from the free clinic, but also the way the Chantry explosion helped them. There could be a few ways that would work I'd have to workshop.
They'd meet up again under much less intense circumstances, and things would progress form there. I've got plenty of sketches about that lol