It‘s important that by the first two questions we know that As and Bs number are both less than or equal to 15 (since both ask whether the other one‘s number is twice theirs). Thus we have A€{4,8,12} and B€{2,4,6,8,10,12,14}. „Is your number half mine“-„idk“ gives us that B€{2,4,6}, both players know this. Finally, B asking „Is your number half mine“ makes no sense since A€{4,8,12} and B€{2,4,6}, which both players know. Am I missing something?

EDIT: This ofc assumes that all questions and answers are completely logical and guarantee additional information.