My problem with this puzzle, is how do you know that Alice and her brothers share both parents?
Is it not correct English to call two people who share one parent, sisters, or brothers?
I guess I could be misguided by my native Norwegian where you have to preamble the word with "hell" (full), or "halv" (half), if you want to specify the number of shared parents.
They would usually be called “half-sisters”. You could call them “sisters” colloquially though but given it’s presented as a logic question I think it’s fine to disregard
It is pretty much the same in English. Unqualified would usually mean sharing both parents but could include half- or step-siblings.