You say "people" but don't specify how many, so for this answer I'm assuming you mean no so many.
Place them on different sides of a huge mountain ridge (like the Himalayas).
The seafaring humanoids come from Vietnam, the Elves from Uttarakhand, The Dwarfs inside the mountains (and maybe surface near Lhasa), The Ferals from Gê'gyai.
That way they have reasonably never met (because their respective living areas are far apart).
Now you start your flood.
The Humans note this first, pack their remaining stuff onto their ships and sail land-inwards towards the mountains they see on good days on the horizon.
The Ferals will notice it second and race for higher ground too (they don't have much to pack, so they are quick).
The Elves notice it third, but are quicker due to their ability to perceive which way is good (being all nature and such). So, they too go for higher ground.
The Dwarfes notice last when their tunnels start to flood. They flee upwards, most likely digging, leaving behind tunnels full of ancient machinery that is now lost forever.
Each and all of them comes to the highest summits in the area which happens to be Mount Everest.
Maybe some Seafarers met other tribes on other summits above 7.500 m (because that's the new sero), but we will never know (until the expansion pack).
The cause of the flood is icy comets raining on earth (in case you don't want it to be actually caused by a God). Or your world had a ocean underneath the tectonic plates and it burst open (then it would be more like a tsunami, then a rain-flood, otoh the biblical flood was a tsunami as well but got reported as rain anyway).