This isn't an in depth answer with references - sorry for breaking the rules.

There are a lot of blurred lines when it comes to delimiting Homo species, and we can almost be considered a single chronospecies since H. erectus. However the basics of it are that the Homo genus evolved in Africa. Then, starting around 600,000 years ago, a splinter of H. heidelbergensis migrated into Europe and Asia, eventually turning into H. neanderthalensis & Denisovans respectively around 250,000-350,000 years ago*.* Meanwhile, H. heidelbergensis populations remaining in Africa were evolving into H. sapiens around the same time. It should be noted that other Homo species existed at the same time as these three, and even bred with each other, but no introgression into H. sapiens occurred.

The first successful migrations of H. sapiens out of Africa occurred around 70,000 years ago, reaching Europe and East Asia around 50,000 years ago. During this period of time, some admixing between H. sapiens, Neanderthals & Denisovans groups occurred, which persists today in H. sapiens as no more than about 10-15% of the genome for particular ethnicities.

Neanderthals & Denisovans then became extinct, while H. sapiens continued to spread into what we know today.

So, in a way, Modern Humans are both relatives and descendants of Neanderthals & Denisovans.

Here is an interesting graph that shows the evolutionary path of the Homo genus