They may be locative.I couldn't find Flaak as a Dutch surname, but Flak, Flake, Vlak, Vlake are close. Flake and Vlake are place names. Vlak means "flat".
I couldn't find Randten as a Dutch surname; nearest were Van Randen and Van der Randen which look like they are from place names. Rand means "edge border" in Dutch, so a locative origin is possible