Personally I pick my battles, I cook healthy food I know ds will eat, it's only in the last couple of years, he's 12 now, that he has become adventurous with food - now he will happily sit and suck the heads of prawns and tuck into a big dish of whitebait.
I stuck to foods he would eat but always introduce something new as a 'just try it and see' option but never as the main course, he could just try what we were having so it removed the pressure.
I wouldn't even bother cooking curry for kids that age OP unless you know they will eat it. Cook the curry for you and grill their portion of chicken.
Sitting down all together and food in the middle of the table is nice too so kids can help themselves to a little or a lot - better than being presented with a plate of food they have to wade through ime.
it's soul destroying cooking food that people turn their noses up at.
You mention the older child used to eat a wider range of food - that's really common, I think their taste buds change or something and they start to get 'fussy.'
One thing I will not tolerate is dramatics or rudeness though, a simple no thank you is sufficient, any wailing about 'being poisoned' is given very short shrift 