How to split the screen with 2 Open Forms inside an MDI

Good morning, everyone. I have a question about Forms. In my application, I can open 2 forms with grids where they display information from the factory. These Grids are updated every 30 seconds, and are opened with:

StartPosition  --> WindowsDefaultLocation.
WindowState --> Normal
Size --> 1002;551

Doubt: I can initialize them by having form1 open maximized, but in the restore button I can resize the Size of it to half the monitor screen? And form2 can identify if there is already an open form and resize Form2 to the second half of the screen with the example below.

Follow the code I'm working on, but incomplete, I'm testing the possibilities so it's not functional, just with a notion. I thought about using the SizeChanged event for this application.

    int lx, ly;
    int sw, sh;
    private void frm_Visualizar_Grid_SizeChanged(object sender, EventArgs e)
    {
        if (this.WindowState == FormWindowState.Minimized)
        {

            lx = this.Location.X;
            ly = this.Location.Y;
            sh = this.Size.Height;

            this.Size = Screen.PrimaryScreen.WorkingArea.Size;
            this.Location = Screen.PrimaryScreen.WorkingArea.Location;
        }
        frm_principal f = new frm_principal();
        if (this.WindowState == FormWindowState.Maximized)
        {                  
            //string cont = Application.OpenForms.Count.ToString();
            string cont = f.MdiChildren.Length.ToString();

            if (Convert.ToInt16(cont) < 2)
            {
                //sw = f.MdiParent.Size.Width;

                this.Size = new Size((sw / 2), sh);
                this.Location = new Point(lx,ly);
            }
            else
            {
                sw = f.MdiParent.Size.Width;
                this.Size = new Size((sw / 2), sh);
                //if (this.Location.IsEmpty)
                f.StartPosition = FormStartPosition.Manual;

            }
        }
    }

Thank you all.

I tried to apply the tip that our friend João Martins mentioned in the answer but did not succeed.

    int lx, ly;
    int sw, sh;
    private void frm_Visualizar_Grid_SizeChanged(object sender, EventArgs e)
    {
        if (this.WindowState == FormWindowState.Minimized)
        {

            this.Size = Screen.PrimaryScreen.WorkingArea.Size;
            this.Location = Screen.PrimaryScreen.WorkingArea.Location;
        }
        if (this.WindowState == FormWindowState.Maximized)
        {
            //foreach (frm_Visualizar_Grid frm in MdiChildren)
            foreach (Form frm in Application.OpenForms)
            {
                this.LayoutMdi(System.Windows.Forms.MdiLayout.TileVertical);
            }
        }
    }