If they already have a freeview tv and are in UHF freeview range for the sake of saving whole lot of hassles . All they have to do is go to a shop and pay $30 or so for an indoor antenna.
Then try it out, if results are poor.. then think of other options.
due to house design/tv location an indoor aerial wont work. I keep pushing to just install a proper external aerial but they don't want to so I'm stuck with looking at other options.
If they don't want an antenna on the roof it can be installed inside the roof.