Hi
The wood will usually clean up nicely with a little work. (aka a lot of sanding)
You can wash it first with TSP to get surface grime off , then a dilute bleach to kill whatever mold is growing then it's time to get out the sander and take it down to bare wood. Much debate over varnish/Cetol/teak sealer for a finish on this site and elsewhere (do a search for all the opinions). My nutshell synopsis 1) Varnish is the most work but looks and lasts the best, 2) Cetol is simple, quick and easy to maintain but lacks the beauty of ten layers of varnish, 3) Oils protect the wood but don't give the shiny, glossy finish some people want. My choice was Cetol. I'd rather spend my time sailing than varnishing.
Warp in the hatchboards seems inevitable over time. A little looseness is necessary to allow for swelling and getting the boards in and out. If they are too loose or warped the easiest fix is to make new ones.
Have fun.
Tom