I've just had someone from the support team confirm this. If you are the "parent" (main) paying account then the features will work properly, but if you have a secondary or "child" account, you can't use the features like Halo Waypoint or the Forza map in Forza Horizon, this is regardless of whether the other accounts are adult accounts or not.
They're offering no fix for this at the moment and all I have been told is that they might fix this with an update at some point.
The only thing I've been told is that if I want to use Smartglass on one of the secondary accounts then I'd have to remove them from the family account and pay a separate subscription for the account that I want to use it on, which totally defeats the purpose of having a family account in the first place.
j4ynut <3 damman33
Met on GR:AW2 05/07, now living together and engaged. :-)