Barnabas exhibited non-vampire related supernatural powers (think his Magic-Number-Of-The-Universe and using the Egyptian Book of the Dead to summon Laura Stockbridge Collins' spirit), so being a vampire doesn't preclude someone from commanding mystical powers, just as being a human doesn't (think Quentin and Stokes).
And so far as Angelique's time traveling powers went, recall that she needed Nicholas' medallion for that, so apparently the power was all in the medallion, and all someone need do was harness it.