Aerial part

Yes you have to drop the headlining.
My advice (i work in an accident repair shop) Remove d pillar trims, where the top of the rear seatbelts come through, Gently slide your hands through to the underside of the roof and undo the nut, keep an eye on the headlining, You don't want to let it crease near the b pillar trims, If it starts to, Remove the b pillar trims aswell.
Hope this helps.