When you say families do you mean Multi-View Parts? Families are for the revit line of products and not for AutoCAD MEP. However you said that you received a dwg and a html package which indicates that it is not a family.
Multi-View Parts consist of a dwg, a xml file, and a bmp file. To add these to an existing catalog you can just drop all three files into a catalog and then inside of AutoCAD MEP type CATALOGREGEN at the command line. This will add the part to the catalog. Some things to consider. If there is an existing part with the same GUID then only the first part encountered in the directory structure will be loaded. You can change the order of the catalogs by going into your Options->MEP Catalogs and then expanding mvparts and moving the catalogs up/down with the buttons on the right. GUIDS by definition are unique and unless you or someone else has already loaded the part or made a copy of it then you shouldnt have to worry about this.
The standard out of the box Multi-View Part catalog is located at C:\ProgramData\Autodesk\MEP 2014\enu\MEPContent\USI\MvParts . This will of course change depending on your version of MEP and if you are using Imperial, Metric, Global...etc.
The process is the same if you are trying to add a duct fitting, pipe fitting, cable tray fitting, conduit fitting, etc.
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