Yeah. Them denisovans etc are all different human species or subspecies. Sometimes they're referred to as archaic humans. Homo means human, and we're talking about other species or subspecies that have art, probably language, tight social structures, some evidence they had seafaring abilities - and our ancestors clearly did interbreed and produce viable offspring - they're human. Feels kinda like a dick move to call them extinct tbh. They had kids, their kids had kids, etc all the way to the present day where they have literally billions of descendants carrying their DNA - like mission accomplished lol what else is a species to do?

Yes, a separate species of humans.

Still humans.

HS are sometimes called "modern humans" to differentiate.

Modern humans still have the exact same troubles with Rh incompatibility, we only learned how to overcome them very recently.