FM,
If the cabin is on the South end of Whidbey, I may be able to help you, but it sounds like you should take OceanSun up on his offer, because there are not many holes like he is describing.
In general, if you launch in Langley, you can go north or south and do pretty good in the bays. Look for pots of the homeowners on the beach. They will start putting them out Friday night in area 8-2. Friday night is by far the best night crabbing. (about 60 feet of water)
If you launch at the Possession Point ramp, you can fish the area OceanSun described, or ones like it.
If you launch in Freeland at Holmes Harbor, you can place your pots pretty much anywhere in the harbor and do OK. If you leave the launch, headout and take a right, you will see other pots. That area is close to the launch and has been pretty good. You can also continue out the shoreline and do well. Commercials have been fishing this area lately too, so...
In area 9, I've not had as good of luck. The exception may be Useless bay, but I don't do that much either. But again, look for the pots of the homeowners, they have the experience.
Watch the tides on these launches, because all are prone to running out of water on a low tide. In langley, you can tie up at the marina and wait for the tide to come in.
Good luck, and PM me if you need something specific.