Where did the Yokudans, or Redguards, come from? Were they Nedes that strayed away and landed on the other landmass? Are they a completely different race of humans that are seperate from the descendents of the Nedes(Nords and Imperials)?
All humans basically descended from the same lot (as did elves if you want to get really technical). The stance I take is that when the lands where reshaped and the oceans formed after the war in the Dawn Era, the Redguard are those that got stuck on Yokuda when the waters came. Others got stuck on Akavir and others on Atmora. Of course there are other explanations possible, I just like this one...
And yes, they are a completely different race from the Nords and such...
Are there any other creatures or mer/men still living on the remnants of Yokuda?
Yes, not all the Yokudan's left for Hammerfell way back in the day so there are still Yokudans on Yokuda; it's just not as big a place as it used to be...
I remember the lighthouse keeper in Anvil saying something about ports of call on Yokuda. What does he mean?
He means that there are trade routes that go to Yokuda best I recall...