help trace Janssen family from Utrecht Holland.

I wish to trace my family. My grandfather Pieter Janssen emigrated to South Afirca from Holland in the late 1920's, his brother Henk also came over. I understand they came from the town Utrecht. Another brother or close relation was a professor of mathematics at the university. I wish to contact any of my relatives. please e-mail me at [email protected]
Regards,
Gavin Janssen.