You must change your Sidelight Dimension(s) to be a "Shared parameter".
After you have changed this "Family parameter" to a "Shared parameter", save and load into your project.
Adding the parameter to the project file:
Go to Settings > Project Parameters... > Click "Add" > Check "Shared parameter" > Click "Select" > Select the appropriate "Parameter group" > Add your Sidelight Dimension(s) parameter (OK) > Select the "Door" category > Group the parameter under "Dimensions" either Instance or Type (your preference)
Adding the parameter to the Door Schedule:
Navigate to your Door Schedule Properties > Edit the "Fields" > You should now see your Sidelight Dimension(s) as an Avaiable field:> Add > DONE and DONE.
Using Shared Parameters are great for schedules *take it a step further and add parameters that indicate all desired Headings within your Door Schedule. First, add them in the family files, then load them into your project file or project tempelates, you will drastically reduce your time of having to fill in the schedule cells, one-by-one. However, in doing this, make sure that you designate which parameters should be "Instance" or "Type"
P A R A M E T R I C components
http://www.parametriccomponents.com [open source Revit Content]
http://www.revitcomponents.blogspot.com [blogging for Revit Components]