If they did not 'sell' the field to the Zhao Family, then Old Master Zhao would spread the rumor that Shao Yunduan assaulted his concubine. As a result, Shao Yunduan's name would be ruined.
At that time, she would act as the victim.
As long as she was inside the house of the Shao Family, no one would know exactly what happened there. She could just make up any story that she liked, and with some extra effort, her Old Master was definitely going to ruin Shao Yunduan's name.
The first section of the family could not afford to make Shao Yunduan lose his future, so they would definitely offer to sell the fields.
Moreover, they would have to sell them at a very low price!
That was a simple method and it should work out well, if it was done properly.
As long as it could work out well, it should be considered as a seamless plan.