I don't think that you can use [man]mysql_num_rows[/man] on more than one query at a time, since you can only count the rows in one table with each command.
I think that you have to do something like this:
//run the query
$result_owner = mysql_query($query_owners);
//query Plots
$query_plots = "SELECT * From $plots ";
$query_plots = $query_plots. "and plot_details($thePlotID) LIKE '$thePlotID%'";
$result_plots =mysql_query($query_plots);
$results= mysql_num_rows($result_owner);
$results2= mysql_num_rows($result_plots);
$item= 0;