There is no way to access the Hidden property of another report item.

You can usually create an expression in the second textbox that evaluates the same as the first one. You are also able to use the ReportItems collection in the visibility expression, so you can reference the value in the first textbox.

For instance if you have this expression for visibility in say Textbox7 -

=Iif(Me.Value = "HideMe", True, False)

You can use this expression for visibility in your other textbox -

=Iif(ReportItems!("Textbox7").Value = "HideMe", True, False)