C# – How to Group Windows Form Radio Buttons

I'm afraid you'll have to handle this manually... It's not so bad actually, you can probably just store all the RadioButton in a list, and use a single event handler for all of them:

private List<RadioButton> _radioButtonGroup = new List<RadioButton>();
private void radioButton_CheckedChanged(object sender, EventArgs e)
{
    RadioButton rb = (RadioButton)sender;
    if (rb.Checked)
    {
        foreach(RadioButton other in _radioButtonGroup)
        {
            if (other == rb)
            {
                continue;
            }
            other.Checked = false;
        }
    }
}

RadioButtons are automatically linked if they are inside the same parent. Since you want them to live in different containers you will have to link them manually.