No. The new husband's daughter would be your stepsister (which I would write "step-sister", but the unhyphenated form apparently is more common, which surprises me slightly). The new husband's sister would, I think, be your step-aunt, though this is not a very commonly heard term.
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Henry74So the relatives of my mother's new husband are not my in-laws. Would you call them step-relatives?H.Some people do use the term "step-relatives". It makes sense to me, and I find it acceptable.