I'm really sorry about your loss, but I thought I'd share an interesting story that might offer a solution to the dog problem.
I have a neighbor that lives up the road and through the woods. Not long after we moved in he and his girlfriend came and introduced themselves as our neighbors and we invited them in. During the course of the following conversation, they told us about Fred, who is not their dog, but lives with them anyway. We were told that the prior owners of their house had abandoned Fred and that they had been providing food, water, shelter and vet care for over a year. They were very adamant that it was not their dog and hoped we wouldn't mind if Fred came to visit us sometimes! About the time we started talking about getting chickens was about the same time that Fred pooped in the middle of our driveway!

un He would come on the property and pee on the generator and the shed and anything else. I called animal control so many times and nothing happened.
The law here says that I have the right to shoot anything that is destroying my property so I did. I bought one of those CO2 powered air pistols that shoots plastic pellets and waited. My dog would start barking when he saw him and I would literally shoot these plastic pellets at Fred and continue shooting until he was out of sight. Fred had such a think mangy coat and was far enough away that I doubt I ever really hit him, but the pellets zooming past scared him enough that he doesn't come here anymore.
I don't know if this would be a good solution to your problems since you would either have to catch them on their way in or get them as they leave. I don't think I'd shoot in amongst the chicks. The dogs don't sound menacing, but I'm afraid this problem will only worsen if not corrected. Can you put up an electric fence, or would your BIL allow his dogs to wear the collar needed for an invisible fence? I hate the thought of losing birds because somebody has a chronic case of the stupids.