Ahhh....family that don't do any mainenance and drive their cars into the dirt....yeah....I have that issue too, hence why I've never bought their cars when they offered them to me...lol. Honestly, you would have no reason to change the plugs early (than what the owners manual says) UNLESS you have misfires or one catastrophically fails (rare)
Yeah haha they are all fucked in the head and believe dealer that you dont change anything itsnlife warranty like transmission and to rarely do oil either bs.
So ill do it at like 100, 000 km along with my timing belt too and that should be it as far as parts to change in 1000s of km to come.
As you know when you buy something brand new 32.5 thousand dollars (financed) with your own money you will take care of it no matter what.
But unfortunately like my older brother with his honda civic of whatever he leased and parents with jeep (financed) and toyota solara (owned years ago but nothing maintained) they all follow dealer nonsense and go to cheap shady bullshit places.
I only take my car to vw approved mechanic never random mechanics that have disgusting shops as where I go to is spotless clean although might be a bit more expensive but hes reliable.