<<Early morning flights often take a southerly route bordering Richmond Park, then later flights are moved to just north of the Upper Richmond Road>>
I suspect that what you are seeing are aircraft landing on both runways, which may occur under certain conditions during early morning.
<< how are navigational systems such as VOR and Satnav used to turn flights into the ILS beam at the right point? >>
All aircraft flying into Heathrow are radar controlled. Instructions from ATC include changes of heading, speed and altitude and the position at which aircraft join final approach varies greatly depending on traffic. It may be 8 miles or it may be 15 miles. To achieve the maximum landing rate, speed control is applied on final approach until aircraft are about 4 miles from the runway.
HTH