Haha. I thought of answering "what matters to them..." which is more natural than "what interests them..." But I eventually translated it literally because I was afraid of losing a heart. It's all DL's fault :)
Oh yeah I remember now.. Is interessa a eles the common way of saying it or no difference?
Does it remain correct if I add the article "o" to "dinherio"? O que interessa a eles é o dinheiro.
"A eles," without the accent, means "to them." The word "à" includes the article "a" and basically means "to the" or "at the." Since there's no article needed here, "à eles" would be incorrect; you wouldn't say "to the them."