why are the sons and daughters so nasty?

Maybe they could have shown nicer relatives but some can't wait to palm off their elderly parent(s) into a home. The old folks are generally nice in my experience and vulnerable when they get to their twilight years - not mentally stimulated always though so not all that communicative in some instances so a little laid back.

I think in this series they just responded well to their carers who were all nice. I loved it when Derek was holding that old lady's hand as she slept.

"These days you have to boil someone before you can sleep with them"

Because nuance is confusing and takes effort to write, so it basically needs to be "inside the care home = Kind, outside the care home = not Kind". Although if you stay in the care home for more than a day or so, Derek will force some Kindness into you - sometimes by brute force (Geoff), or sometimes just by being around (rapper guy).