It appears as though that form is a sibling of those other child controls. Do you have to open it as a child of that window? Can't it be like a non-modal dialog box and not a child window of that main form?
If it has to be within that main form and a sibling of those controls, then you're going to have to set the Z-Order of it. There's no property for that, so you're going to have to look toward the Win32 API call, SetWindowPos
:
[DllImport("user32.dll", EntryPoint = "SetWindowPos")]
public static extern bool SetWindowPos(
int hWnd, // window handle
int hWndInsertAfter, // placement-order handle
int X, // horizontal position
int Y, // vertical position
int cx, // width
int cy, // height
uint uFlags); // window positioning flags
const uint SWP_NOSIZE = 0x1;
const uint SWP_NOMOVE = 0x2;
const uint SWP_SHOWWINDOW = 0x40;
const uint SWP_NOACTIVATE = 0x10;
And call it something like this:
SetWindowPos((int)form.Handle, // that form
(int)insertAfter.Handle, // some other control
0, 0, 0, 0,
SWP_NOMOVE | SWP_NOSIZE | SWP_SHOWWINDOW | SWP_NOACTIVATE);