The images will adapt to the document width if the images are larger than the page width to start with, however smaller images will not.
The reason your code stacks the images is that you are converting them to shapes and adding a wrap option, for some reason which is not entirely clear, and then you are not repositioning the shapes. I see no reason to change them to shapes. The following will set your margins (though you could have done that before inserting the pictures) and will set the width to the width between the margins. As it is almost inevitable that there will be room for only one image on a page they will then be on separate pages.
Code:
Sub ResizePic()
Dim x As Integer
Dim lngWidth As Long
With ActiveDocument.PageSetup
.LeftMargin = CentimetersToPoints(1)
.RightMargin = CentimetersToPoints(1)
.TopMargin = CentimetersToPoints(1)
.BottomMargin = CentimetersToPoints(1)
lngWidth = .PageWidth - .LeftMargin - .RightMargin
End With
For x = 1 To ActiveDocument.InlineShapes.Count
ActiveDocument.InlineShapes(x).Width = lngWidth
Next x
End Sub