The 1978 NSW mare Souriboe had 16 foals for 13 winners of a total of 133 races through the 80's and 90's mostly in the Sydney area, I would be surprised if there not a few nights where 3 or more were at the same meeting but I can't tell you Katie, that mare was some sort of producer though, average of 10 wins per winner and 13 individual winners in total would be hard to better in itself I'd reckon.
cheers,
Danno