What relation to you is your half brother's half sister?

Answer 1

Your half-brother's half-sister could be your full sister, or not related to you at all.

For example, say your parents are Joe and Mary and your half-brother's parents are Mary and Steven. Say your half-brother's half-sister is Barbara.

If Joe and Mary are Barbara's parents, then she is your full sister and your half-brother's half-sister. If Barbara's parents are Steven and Jane, then Barbara is not related to you (unless there is an adoption).