It sounds like your chickens are running loose in your yard. If so, the problem isnt the neighbors dog, its your containment, or lack of. If their dog can come over and get to your chickens, so can any other dog. You, or they, may take care of that dog, but it won't be the last loose dog you'll likely have to deal with.
Do not worry and fret and pout over what you can not control. All you can control is your birds on your property. Make them safe from any predators, including loose dogs. The only thing you can do with that dog is call animal control, if you have one, or catch it and take it to the pound. If you're not willing to do that, and your in-laws arent willing to contain their dog, you will be in for a lot of misery in your life for a long time unless you contain your birds. Its your choice.
Do not worry and fret and pout over what you can not control. All you can control is your birds on your property. Make them safe from any predators, including loose dogs. The only thing you can do with that dog is call animal control, if you have one, or catch it and take it to the pound. If you're not willing to do that, and your in-laws arent willing to contain their dog, you will be in for a lot of misery in your life for a long time unless you contain your birds. Its your choice.