You cannot set TargetProperty in Style Trigger. This basically means that you should create a custom control derived from StackPanel which contains two checkboxes and these checkboxes are exposed as properties. Then you'll be able to define a style for that control (not the CheckBox) and set the properties you want.
Much easier way (if only needed for testing) would be this:
<StackPanel>
<StackPanel.Resources>
<local:InverseBoolConverter x:Key="InverseBoolConverter"/>
</StackPanel.Resources>
<CheckBox x:Name="chk1" Content="CheckBox1"/>
<CheckBox x:Name="chk2" Content="CheckBox2" IsEnabled="{Binding ElementName=chk1, Path=IsChecked, Converter={StaticResource InverseBoolConverter}}"/>
</StackPanel>
Where InverseBoolConverter is defined as follows:
[ValueConversion(typeof(bool), typeof(bool))]
public class InverseBoolConverter: IValueConverter {
public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
if(value is bool)
return !(bool)value;
else
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) {
if(value is bool)
return !(bool)value;
else
return null;
}
}