Complex sentence: These claims have never been confirmed by the Davis or Sanchez families; therefore, many people consider them to be speculative, and believe it best to rely on Sammy Davis Jr. himself as the source for his mother's origins.
Split into simpler sentences: These claims have never been confirmed by the Davis or Sanchez families, and therefore continue to remain as speculation. Therefore, many people believe it best to rely on Sammy Davis Jr. himself as the source for his mother's origins.