Rem and Joey's relationship should be discussed more as it directly parallels Vash and Knives' relationship in so many ways and it's highlighted so effortlessly in the first minute of episode 17.
The sub differs slightly as Rem asks plainly:
The fact that Rem completely ignores Rowan's analysis, asks Joey this question, and Joey dismisses Rowan again to give her some hope that there might be flowers on the planet, speaks on just how weird their dynamic is. Rem is able to turn away from reality/tangible facts because of Joey's status as the ship's captain. Additionally, because of her proximity to Joey and his authority, Rem gets to maintain her rose colored view of the world/future with no one to contradict her and avoid Steve's sexual harassment. So even though there is tangible evidence that her Eden may be impossible to achieve (Steve sexually harassing/assaulting Mary and verbally abusing her sons in front of her), Joey allows her to exist in this perpetual fantasy where she can blatantly ignore what's happening in front of her. That way her Eden remains intact. It's a fantasy that she engulfs Vash into, one so all consuming that it borders on/is emotional incestuous in nature.
But Knives' relationship to Rem is relatively non-existent. They share like three scenes with each other but each lacks the same intimacy she has with Vash. That's likely because while Vash had Rem, Knives had Joey, whose clear logic clicked more for him than Rem's emotional arguments. But that's the thing. Joey's logic is tempered by his affection (love?) for Rem. It twists and bends to make room for her fantasy. And in turn, Knives follows Joey's example and uses his logic to provide Vash solace that Rem's Eden is possible after Vash is abused by Steve.
Later, after Knives is also abused by Steve, he speaks with Vash as he doesn't believe they'll be protected in Rem's Eden. Vash disagrees and uses Rem's sentimentality as a weak counter argument. It's here that Knives rationalizes that Rem philosophy will not protect them for the discrimination ahead of them. (Moreover, this is the exact moment Knives begins to absorb both Joey's logic and Steve's racist abuse to form his own outlook on the world. It's an outlook that defines him for the rest of the series (most clearly seen in episode 24 in his monologue to Chapel*) and in this way, he is as much a child of Steve as he is Joey.)
So Knives clings to hard logic instead and when he sees that Vash wants to solve a problem (save the butterfly from the spider) he acts for his brother to Vash's anger.
This is Knives taking the next step in Joey's outlook by assuming what Vash wants and doing it. Knives then chooses to not coddle Vash by forcing him to grapple with reality of the situation. It's parental and blurs the boundary of their sibling bond. (It's also his first attempt to take Rem's role in Vash's life. Knives does so definitively when he killed Rem's last living relative in episode 26 to cut off Vash's dependence on Rem and her legacy.)
And when Rem protests, Knives argues against her sentimentality and, with no one to back up her worldview, Rem can't respond effectively.
Vash proceeds to counter Knives' logic by tackling him, using physical violence to shut him up. (This introduces violence to Rem's Eden and foundationally changes their relationship.)
And when Knives plots with Rowan and Mary to take out Steve, Rem and Joey's relationship begins to change as well. When Mary accuses Steve of rape, Rem begs for a fair trial. But Joey can no longer coddle or give credence to Rem's sentimentality because of the severity of Steve's charges (spiders eat butterflies.)
Things escalate when Rowan tells Mary he murdered Steve so that they could be together only for her to refuse his advances. Rowan then kills her. And when Rem takes a step of faith to get the gun out of Rowan's hands, Joey, terrified that she could die, makes the decision to open the air lock and kill Rowan (killing the spider to protect the butterfly.)
But unlike Knives who remains resolute in his logic, Joey falters. He lets his sentimentality (love?) for Rem cloud his judgement. Could Rem have taken the gun? Did he make the wrong choice? And Knives kills Joey for doubting himself and to affirm that he's making the right choice.
The weirdly parental bond Knives develops because he takes after Joey (and Steve) is the throughline for his relationship with Vash and why they misunderstand each other.
Because while Knives' logic driven paternalism** is obviously bad and dismissive of Vash's agency, Vash's rose colored view of the world where he can consistently step in to stop violence without killing every time/being 100% beholden to Rem's pacifism at the cost of his body and life is bad as well. The only way for their feud to tangibly end is for Vash and Knives to both give up their parent's logic/worldview and decide for themselves how they want to act as Vash concludes in the final episode. And by not killing Knives he gives him the chance to do just that.
(If you want a full breakdown of Vash and Knives's relationship/psychologies I've already written a full essay on the subject here!)
Some footnotes below!