I definitely think Stek and Aty came to love her, especially with the framing we’re given from an outsider. The old woman cannot comprehend why Stek did what he did, and assumed his smile in his final moments had to be him going insane.
However, with how many excuses they told themselves to keep her, the fact that we know Saidda was allowed to play with other kids and have friends and other things which would be “unnecessary” for a cash cow (which the old woman never mentions her friends, but we see the effects of in the present), and that Saidda still wants to stay with them despite hearing what they say about her implies she can see past it, I really do think Stek’s last stand was entirely out of love for Saidda, even if he would never admit it.
Especially since Silver Mountain as a whole so far has been about the uses of strength and force, even from the early chapters of Ginbei hating soldiers and stopping needless violence, I think Stek’s last stand being out of his love for Saidda and trying to protect her just emphasizes that narrative perfectly.