Regarding ownership of the land that they stand on (Haylands) I would presume it belongs to Hanson's the Quarry owners.  The only mention of ownership of the windmills I can find is in a book Portland Encyclopaedia written by Rodney Legg. It mentions that they were originally owned by the Pearce family and probably built in the 17th century.  He also names them as, i.e. the windmill covered in ivy (Northern Windmill) is called Angel Mill and the other one, the other side of the field is called South Mill.

It is kind of you to accept my pictures for your site, I hope people enjoy them.