When Candace says she and her brothers were "Great friends" to Amanda in Quantum Boogaloo, all things considered she wasn't wrong. As far as 15 year old sisters and 10 year old brothers go they are very close.
She may often get upset with them, but they rarely do at her, and Candace's ire with them doesn't always process in their minds. They don't actually argue often, and when they do its usually pretty brief and quickly addressed.
Candace CHOOSES to spend time with them, doing things like playing skiddley whiffers and watching movies with them. (Which is a lot all things considered for two sets of kids at different stages in their life with different interests). Not to mention the big ideas, like circumnavigating the globe, and going to space, and singing as pop stars. And they do things like trick out a car for her and build her a phone and build her a rocket ship for her just because.
Not to mention that single summer isn't really reflective of their WHOLE childhood. It's definitely meant a joke, adult Candace looking back with rose colored glasses, but in all fairness, we the audience only have a snapshot of at most a year of their childhood. And even within that snapshot we see that, yeah, for all that the show focuses on Candace's beef with her little brothers, they get along really well.
That said, it is definitely the pot calling the kettle black because it's not as though Amanda gets along any worse with her brothers than her mom and uncles. We see less of Amanda, but all things considered it does seem that her beef with her brothers is relatively one sided. It seems that she WANTS to spend time with her brothers. They just don't want to do anything.
