Informatie gezocht

I own two paintings by Jan Knikker. One is a Polder scene and the other os of a road by a river with a church in the background and people walking on the road. They are signed Jan Knikker in bold letters in the right hand corner. I found a similar painting on a website of Sovereign Collection's Home paintings on the AltaVista website. It is signed Jan Knikker Sr. (1889-1957) $7,500 USD. Couldn't get any other information. It also was a polder scene. Would love to find out more about my paintings; what their value is and how to put them up for sale. I also know that Jan Knikker went to the Hague school.
In much appreciation,
Petronella Vasconcellos Groenendijk