This is a bit of an overreaction, in my opinion. There is nothing actually explicit happening. Some wordplay for adults to be amused by, sure. Even kids' movies these days often slip in sly humor that parents chuckle over, but that flies right over the heads of children. There are much more effective ways of parenting than trying to censor everything around you. That will simply breed ignorance instead of understanding. There's nothing crude about the phrase "sofa king" unless you choose to read it that way, and there's no reason why you can't explain to your kids the literal and perfectly innocent meaning. After all, do you censor "Chickamauga Dam" because it happens to have the same pronunciation as another four-letter word?
In the end, it's just a name of a restaurant that makes about as much sense as any other name of a restaurant. I have to agree with the owner: if you see something shocking and vulgar here, it probably has more to do with your perception of the world than a burger joint's sign.