Earliest ancestor of humans who could integrate into modern society
Interesting question.

The organism would have to be monogamous, that's for sure, otherwise it would be too competitive and it would be a beast - as chimps are. Chimps couldn't integrate into the modern society.

So, monogamy is the prime prerequisite as it's also prerequisite for intelligence. Bipedalism is another obvious prerequisite, as you need an organism with fine motorics of front limbs - and fingers.

For "modern language" you need high intelligence and the ability of abstract thinking. Same goes for reading and writing.

Humans split from great apes between 8 and 4 million years ago. Problem here is that every new piece of fossil of a human ancestor is classified as a new species, so there's very little we're certain of. I'd say the first organism capable of doing the above things existed around 200.000 years ago. Either homo erectus or, more likely, a Neanderthal.