Huibrecht gives Breggie in Afrikaans and should logically give Bregje in Dutch. Either way, it's a female form of Hubert. You're right: that -je is a diminutive ending. Bertie, perhaps? As for pronunciation, my Dutch is mangled but it's close to a short e as in bed, followed by that wonderful throat-clearing sound that is always said to be "like the -ch in Scottish loch", and a ye, same short e as before, and the j has an English y sound.
Can't help at all with Ms Prinsloo, but a lot of white Namibians have Afrikaans surnames, of which Prinsloo is one. I'd guess bi-HAH-ti, but it is a guess and the name looks invented.