How to call Same event Handler with multiple class object in Windows form C#

Question

I am creating class with event and delegates. Now I want to call the same event handler with multiple class objects at a same time. How can I do it.

My Event Class

public class TimerClass
{

    public delegate void NumberIncrEventHandler(object sender, NumberChangeEventArgs e);
    public event NumberIncrEventHandler NumberIncr;
    private int counter = 0;
    private bool _isStop = false;

    public TimerClass()
    {

    }

    public void start()
    {
        for (int ctr = 0; ctr <= 10; ctr++)
        //while (true)
        {
            if (!_isStop)
            {
                counter++;
                Thread.Sleep(1000);
                NumberChangeEventArgs e = new NumberChangeEventArgs(counter);
                OnNumberReached(e);
            }
            else
            {
                _isStop = false;
                return;
            }
        }
    }

    public void stop()
    {
        _isStop = true;
    }

    protected void OnNumberReached(NumberChangeEventArgs e)
    {
        if (NumberIncr != null)
        {
            NumberIncr(this, e);
        }
    }

}

public class NumberChangeEventArgs : EventArgs
{
    private int _reached;
    public NumberChangeEventArgs(int num)
    {
        this._reached = num;
    }
    public int ReachedNumber
    {
        get
        {
            return _reached;
        }
    }
}

And In my form code is like,

  public partial class frmStartStop : Form
  {

    public ControlClass.TimerClass ctrl1 = new ControlClass.TimerClass();
    public ControlClass.TimerClass ctrl2 = new ControlClass.TimerClass();

    public frmStartStop()
    {
        InitializeComponent();
        ctrl1.NumberIncr += new ControlClass.TimerClass.NumberIncrEventHandler(this.ctrl1_Tick);
        ctrl2.NumberIncr += new ControlClass.TimerClass.NumberIncrEventHandler(this.ctrl2_Tick);
    }

    private void btnStart2_Click(object sender, EventArgs e)
    {
        ctrl2.start();
    }

    private void btnStop2_Click(object sender, EventArgs e)
    {
        ctrl2.stop();
    }

    private void ctrl2_Tick(object sender, NumberChangeEventArgs e)
    {
        txtCount2.Text = e.ReachedNumber.ToString();
        Application.DoEvents();
    }

    private void btnStart1_Click(object sender, EventArgs e)
    {
        ctrl1.start();
    }

    private void btnStop1_Click(object sender, EventArgs e)
    {
        ctrl1.stop();
    }

    private void ctrl1_Tick(object sender, NumberChangeEventArgs e)
    {
        txtCount1.Text = e.ReachedNumber.ToString();
        Application.DoEvents();
    }

    private void btnExit_Click(object sender, EventArgs e)
    {
        Application.Exit();
    }


}

Now when I run my application both tick events are not working individual. So, What I need to do to run individual event.