For two or more controls you need to reset the range position after inserting the controls e.g. as follows. You can follow the process for more controls as required.
Dim oCC As ContentControl
Dim oRng As Range
'Set a range where you want the first control
Set oRng = Selection.Range
'Ensure that the range does not include a selection of text
oRng.Collapse 0
'add a content control to the range
Set oCC = ActiveDocument.ContentControls.Add(wdContentControlRichText, oRng)
oCC.Title = "This is a great block!"
oCC.Tag = oCC.Title
Set oRng = oCC.Range
oRng.InsertFile ("E:\Templates\Template Building Blocks\block1.docx")
'Move the end of the range out of the control
oRng.End = oRng.End + 1
'Collapse the range and type a space
oRng.Collapse 0
oRng.Text = " "
'Collapse the range again and add another content control
oRng.Collapse 0
Set oCC = ActiveDocument.ContentControls.Add(wdContentControlRichText, oRng)
oCC.Title = "This is another CC"
oCC.Tag = oCC.Title
Set oRng = oCC.Range
oRng.InsertFile ("E:\Templates\Template Building Blocks\block2.docx")
If you want to insert both texts in the same control, the method is similar e.g.
Dim oCC As ContentControl
Dim oRng As Range
'Set a range where you want the control
Set oRng = Selection.Range
'Ensure that the range does not include a selection of text
oRng.Collapse 0
'add a content control to the range
Set oCC = ActiveDocument.ContentControls.Add(wdContentControlRichText, oRng)
oCC.Title = "This is a great block!"
oCC.Tag = oCC.Title
Set oRng = oCC.Range
'Insert the first file
oRng.InsertFile ("E:\Templates\Template Building Blocks\block1.docx")
'Collapse the range and type a space
oRng.Collapse 0
oRng.Text = " "
'Collapse the range again and add another text
oRng.Collapse 0
oRng.InsertFile ("E:\Templates\Template Building Blocks\block2.docx")