Some people don't like dogs in their homes, my sister never used to let my first dog or my following dog in her house as she reckoned it would upset the cat, I would have to leave it in my car. When she got a dog 2 years ago suddenly she decided that dogs should be welcome everywhere, including other relatives who don't like dogs and have cats. When she brings her round my house it always deficates on my garden or several times in my house, her attitude is well I was in a rush to come and didn't get a chance to walk it! I agree with others, if you turn up at someone's door with a dog, its inferred that you hope to bring it in, saying you are willing to take it home again would make the householder feel uncomfortable, especially if you are telling them you had brought it with you to show his wife, so you were expecting to go inside with it. Some dogs are excitable, new dogs are an unknown, you have said sil cant go out alone, so bil might think the risk of an unknown dog jumping about is too great. Try going back round and explaining you hadn't thought it through and not to let it spoil your relationship