You can open multiple instances of a single form in MDI form. Below is some sample code where Form3 is a MDI parent form and Form1 is a MDI Child form.
Code:
Public Class Form3
Private Sub Form3_Load( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs _
) Handles MyBase.Load
Dim frm1 As New Form1
frm1.MdiParent = Me
frm1.Show()
Dim frm2 As New Form1
frm2.MdiParent = Me
frm2.Show()
End Sub
End Class
To show multiple reports, just create a single form with ReportViewer control, create multiple objects of this form and provide the necessary details to load the reports. That's the way how it should be done.