Auto-resize multiple Forms rendered on Panel

Solution 1:

After some clarifications, it appears that the desidered layout and behaviour of the described Form is similar to this sample disposition:

A WinForms Form is embedded in another Form, and placed inside a Panel.
This Guest Form is stripped of its TopLevel coat-of-arms and parented to central Panel, as shown in this graphic example:

How do you dock these Panels to get this layout:

The Green Panel stays on top of the Form.
The DarkGray Panel lays on the left hand side of the Form.
The Gray Panel occupies the remaining space.

• Insert three Panels on a Form container.
  
• The Green Panel needs to maintain its position, it will never change:
  
  • Right click → SendToBack (!important :).
    
  • Dock → Top.
    
• The DarkGray Panel is positioned under the Green Panel, on the left side of the Form. It needs to resize itself when needed, but will never cover the Green Panel:
  
  • Dock → Left
• The Gray Panel needs to occupy the remaining space. It needs to resize itself when needed, but it will never cover Green Panel or Dark Gray Panel:
  
  • Right click → BringToFront (!important)
    
  • Dock → Center
    

The highest priority when docking, is assigned to the element which has the lowest z-order in the stack: the Green Panel, here. The lowest priority is assigned to element with the highest z-order: the Gray Panel, which will then shrink and stretch among all other elements with higher priority (following the z-order).

How to embed the Form:

The easy part. It's a Form in our Project, no need to perform any magic to keep it alive when re-parented:
(This is just for 1 Form. With more Forms, you'll need something like a List<Control>:

//Define here the Form which will be embedded
[Your Form Class] EmbeddedForm;

private void button1_Click(object sender, EventArgs e)
{
    EmbeddedForm = new [Your Form Class]() {
        TopLevel = false,
        Parent = panContainer,
        Location = new Point(4, 4),
        Enabled = true
    };
    EmbeddedForm.Show();
}

private void buttonShrink_Click(object sender, EventArgs e)
{
    //Maybe insert a classic dotted mini-button to re-inflate the sidebar when needed
    panelSideBar.Width = 6;
}

private void panelContainer_Resize(object sender, EventArgs e)
{
    Rectangle rect = panelContainer.ClientRectangle;
    rect.Inflate(-3, -3);
    EmbeddedForm.Size = rect.Size;
}

If you allow your Container Panel to AutoScroll its content, the Resize event is not necessary.

Edit:
A PasteBin of the complete source code of the Form in sample graphics: Embedded Forms