That post about how Angeal is willing to steal from people who are poorer than Genesis's family made me remember a theory I bombarded @birdblacksocialclub with ages ago, so I want to have a little ramble about it here.
Angeal says he would not steal from the trees belonging to Genesis's (foster) family because they're friends. it would be dishonourable to steal from your friend. But I have another theory about where this line of thinking came from other than Angeal's sense of honour.
One of the few things we know about Genesis's foster parents is that they were reporting back to Shinra, albeit they later chose to lie to them when they 'got attached' to him. Notably, Gillian (Angeal's mother) chose not to and refused to let Shinra anywhere near Angeal save for the existing surveilling that was being done in Banora. This makes total sense, she tried to leg it with him as a baby and was caught, so she clearly didn't want Shinra involved with Angeal in a big way and refuses to acknowledge anything about her life in the Jenova project.
Genesis and Angeal are childhood besties. It's likely they were in and out of each others pockets, but the economic difference between them had to mean that Genesis was more likely to want to give him things. Unfortunately, those things came via his foster parents and by extension, Shinra - the very company Angeal's mother is trying to get to leave him alone to live out his life relatively quietly.
My bet is that Gillian told tiny Angeal that he shouldn't take things from Genesis, that it isn't honourable, that it was considered charity and they had some pride and he internalised that as not taking things from his friend. From his perspective, the issue is that they're friends and it's a matter of respect and pride between them.
From Gillian's? It's trying to make sure
a) Angeal is not in Shinra's debt due to Genesis not understanding where his foster parents loyalties once lay and he's more likely to stop offering if Angeal is the one to shut it down than if she does
b) instilling the idea that Angeal shouldn't take things from people in power because it might land him in some trouble some day, especially if she's wary of someone of the suited variety showing up one day
and c) that said foster parents don't see enough of Angeal to ever include him in their observations because she knows they're not normal kids
(those blueprints for the copy tech were archived with Project G, they absolutely knew when they were kids that they had some abilities, just not enough as to be as sure a bet as Sephiroth was)
It might have been about honour for Angeal but I think it probably started as a way to try and keep him away from Shinra's scope. At least, until the war kicked off and he signed up anyway.