merfolk they are seadwelling makes little sense. same with the overlords.
The Merfolk, granted, don't seem -too- sensible (unless, mayhap, it refers to a more amphibious version that -is- capable of walking on land). The Overlords (that is, the race and not the religion) are not of this world though; from what I recall of Age of Wonders II, they're from the depths of the shadow dimension, I think, though here they could be just about any form of colonists from deeper dimensions of time and space and so forth.
how about an amphibous race like frogloks give them the ability to travel in water with the melee forces
Currently, the Drown already have such an ability, I think. I'd imagine a frog-like race might have such an ability for their UU, perhaps?
the undead this again makes no sense since undead dont breed or try to make weapons again no sense.
They don't breed but they -do- increase their numbers; they put corpses to work, bring forth the souls of the departed and give the dead life. They reproduce from the dead of others, essentially, through necromancy and so forth. Additionally, they also obtain followers, supporters and cultists of other races, seeking purpose, power or immortality.
ugly and gross for the undead their are lots myabe ogres or trolls would work
Why would it have to be 'ugly and gross' exactly?
also is their a way to change the abrbarians names to unussed races?
I think I prefer Barbarians representing nomadic tribes, bandits, pirates and so forth. That said, perhaps it'd be possible to have barbarian units more akin to bandits, picking on lone travelers and so forth and aiming specifically to pillage whilst avoiding direct confrontation with cities (lowered city strength akin to Assassin?) whilst others are direct city raiders.
should centaurs be able to build mounted units from the start?
That'd be a bit advantageous early game but, once spears come about, it quickly becomes highly unfair against them as their units would easily fall to spears.
Edit:
One final point- is it possible to get the Workboat to upgrade to some kind of Tug or sea-going vessel? It really ticks me off when I actually get whales within my city limits in the sea but I -can't- get my Workboat out to build some whaling vessels.