Stepsiblings are children born of two different families who have been joined by marriage, defacto or otherwise, of at least one of their respective.
English has no name for a stepsister's halfbrother but try drawing the relationships in diagrammatic form, rather then describing them in words.
A stepfather, a stepmother, a stepbrother or a sister are all social relationships without common genes. A halfbrother or a halfsister, unlike stepsiblings.
Yes, the title of a step brotherinlaw is given to your stepsister's partner AND to the stepbrother of your partner. A stepsister is the daughter of your.