I have heard 2 different origins for the name Dweck (all Dwecks are related regardless of spelling, and that includes the French Doueck spelling and Spanish Duek). One, which makes sense because Arabs have it as well, is goldsmith. The other is that it comes from the same root as “duke” through Latin and it was a Spanish title.
In any case, whoever took it was a Cohen; the name has nothing to do with kehuna (and Solomon notwithstanding, nothing to do with a similar unpleasant Yiddish word either).
Rapaport is an acronym for Rofe da Porto, and while there are Rapaports who have the name and are not Cohanim, the original Rav Meir Rofe da Porto was a Cohen. The non-Cohanim have it either from mothers (widows sometimes passed down family names due to bureaucratic error) or Ellis Island.