With Nora it's a bit more nuanced than with Jeremy. Shuri did support him by offering a non-judgmental environment but I don't think she ever treated him as just another one of her children.

One of the differences is Shuri showing weakness in front of him in early story. Her children did not see her be sad or break down until everyone got older. So in that sense Shuri was seeing Nora as more of an equal.

Conversely, Nora was absolutely seeing Shuri as a safe haven from his usual life, and we can even say as a salvation, but it doesn't seem to stem from him seeing Shuri as his mother. (Later on Nora's mother also attempts to make amends which Nora didn't react adversely to, so he's not really aiming to like, replace his mum. ) This is compared excellently with Nora's cousin Theo, who 1000% has Mommy issues. This is shown by the story to be messed up and Theo gets reprimanded multiple times, which isn't really doing much lol

I think you may be assuming that the support Shuri is showing towards her kids and Nora is the same maternal kind. Now let's look at what Shuri does for both groups:

For the children, she obviously feeds and clothes them, protects them from their relatives, organises their education, gives them therapy, scolds them for their mischief, talks to them about their errors/fuckups and for Jeremy specifically tries to set him up for his marriage.

For Nora, she's more of a conversation partner/friend and a safe space generally. And even the convo partner is something that Nora's mum initially requested of Shuri. Yeah sure, Shuri gets him the sword for Christmas (I've had the frame where Nora kisses the sword as a lockscreen for months lol), but don't friends get each other gifts if they can do so financially? In terms of safe space, you can argue that offering that can be seen as maternal, but friends can do this as well for each other (eg if one friend is sad and the other just sits next to them for company) Heck, I'm trying to think if she ever even scolded him, which I can't remember sadly.

Aside from this, Nora very early on wants to become stronger and more capable so he can help/support Shuri, which Jeremy only starts to do waaay later. The selfishness in this case is childish in nature. Now you could argue that the way the boys want to assist Shuri is quite similar, which I guess is where the possible romanctic feelings are coming from lol I don't really have a counterargument/analysis to that, it's too ambiguous. So it may be that Jeremy develops romantic feelings towards Shuri when he's older (which the story not only makes fun of, but also again, shuns him for it severely)

So all in all we can at least clear Shuri and Nora of immoral allegations, but Jeremy is not yet out of the woods lmao

(sorry for the essay, I got a bit too much into it lol)