how long was alucard with the the siblings

Alucard was not actually with the siblings as a canon relationship in the main Castlevania material; the most relevant source here says Alucard and Harith are not related , and Harith became more of an ally/adopted younger brother after Alucard saved him. If you meant a different “siblings” pair from a forum thread or another adaptation, the wording is too ambiguous to pin down a duration from the available source.

What the source suggests

• Alucard and Harith are described as coming from different families, not as blood siblings.

• The relationship is framed as ally/adopted-brother rather than a timed “with the siblings” situation.

• A Reddit discussion also notes that a similar pair people ask about were “not siblings,” which points to common fan confusion.

Simple takeaway

There isn’t a verified length of time for “Alucard with the siblings” in the source I found, because that specific sibling claim doesn’t hold up in the material returned here.