Do you really think, these brothers, who has absolutely loved no one before, can on their own, understand the concept of "I'm only happy if my loved one happy"?
I mean, yes? Like, it's precisely because they seem to understand the gravity that emotional bonds hold that they keep themselves separated. So that they don't end up loving each other and then end up killing or being killed by one another. If they understand that then I think it's fair to assume that they understand the concept of it.
That said, understanding something and being consciously aware of it are two different things. Still poor planning on their part.
I just think that it's poor planning on their part to not treat Theo like he has a higher status. No matter how you spin it, it's obvious that Chloe wouldn't be happy about her only friend being a servant while she lives the high life. She wasn't raised as a noble so she isn't gonna go "Oh, well we obviously hold different ranks." She's thinking, "Wow, so this is how people who say I'm so important treat my best friend?!"
In a society like their's, special treatment is okay when the situation demands it. This the situation. Like, how many stories like this are there where the nobles literally buy titles?