XAML mukti单选按钮组和标签

嗨，我是xaml新手，我试着读过一些样本，但我迷路了

现在我有两个问题

我希望标签文本首先在按钮之前，文本与按钮文本对齐，或者有标签文本、换行符，然后是按钮

我无法使这两个单选按钮组的默认值处于选中状态。只有最后一个组设置了ischecked=true，第一个组被忽略

所以请帮助我，我有点不对劲，我不知道那是什么：(

#96d1ff

<ContentPage.BindingContext>
    <vm:AboutViewModel />
</ContentPage.BindingContext>

<ContentPage.Resources>
    <ResourceDictionary>
        <Color x:Key="Accent">#96d1ff</Color>
    </ResourceDictionary>
</ContentPage.Resources>

<Grid>
    <Grid.RowDefinitions>
        <RowDefinition Height="Auto" />
        <RowDefinition Height="*" />
    </Grid.RowDefinitions>
    <StackLayout BackgroundColor="{StaticResource Accent}" VerticalOptions="FillAndExpand" HorizontalOptions="Fill">
        <StackLayout Orientation="Horizontal" HorizontalOptions="Center" VerticalOptions="Center">
            <ContentView Padding="0,40,0,40" VerticalOptions="FillAndExpand">
                <Image Source="xamarin_logo.png" VerticalOptions="Center" HeightRequest="64" />
            </ContentView>
        </StackLayout>

        <StackLayout>
            <StackLayout>
                <Frame BackgroundColor="White" BorderColor="Black">
                    <Grid ColumnDefinitions="*,*,*" ColumnSpacing="10" x:Name="Grid1">
                        <!--<Button Text="t1"></Button>-->

                        <Label Text="Radio button group 1" HorizontalTextAlignment="Center"></Label>

                        <RadioButton IsChecked="True" Content="None"  BackgroundColor="White" GroupName="Group1" />
                        <RadioButton Grid.Column="1" Content="Light"  BackgroundColor="#F0FF00" GroupName="Group1" />
                        <RadioButton Grid.Column="2" Content="Moderate"  BackgroundColor="#ffba08" GroupName="Group1" />
                        <RadioButton Grid.Column="3" Content="Severe"  BackgroundColor="#dc2f02" GroupName="Group1" />
                    </Grid>
                </Frame>
            </StackLayout>

            <StackLayout>
                <Frame BackgroundColor="White" BorderColor="Black">
                    <Grid ColumnDefinitions="*,*,*" ColumnSpacing="10" x:Name="Grid2" >
                        <Label Text="Radio button group 2" HorizontalTextAlignment="Center"></Label>
                        <RadioButton IsChecked="True" Content="None"  BackgroundColor="White" GroupName="Group2" />
                        <RadioButton Grid.Column="1" Content="Light"  BackgroundColor="#F0FF00" GroupName="Group2" />
                        <RadioButton Grid.Column="2" Content="Moderate"  BackgroundColor="#ffba08" GroupName="Group2" />
                        <RadioButton Grid.Column="3" Content="Severe"  BackgroundColor="#dc2f02" GroupName="Group2" />
                    </Grid>
                </Frame>
            </StackLayout>
        </StackLayout>
    </StackLayout>
</Grid>