possibly re-homing our dog

[squiddles]

Kinda long, bare with me lol

About two and a half years ago we adopted a sweet dog named Brody from church friends of ours, (he had been chasing and attacking their chickens so they couldn't keep him), he is a lab/greyhound mix. He is now 10 years old, and could potentially live another couple years or more.
He is in excellent physical health, but he seems to be bi-polar (if that's possible for dogs). He bounces back and forth between incredibly depressed, to unbelievably happy. All we know about his history is this:
Birth-2years: unknown/shelter
2years-4years: owned by John, who trained him incredibly well, he was a fantastic owner, we met him and have gotten to know him, he comes over to visit and give us training tips, he rehomed Brody because his work hours were too long and Brody was needing to stay crated for up to 14 hours during the day, and was seeming to be very depressed by this.
4years-7years: Brenda's family (from church)
7years-now: us

We have speculated that during Brody's first two years he must have been abused, because he does not like most men, and he cowers in fear (serious shaking fear) when there is tension in the room. He couldn't handle the baby crying or me hollering at the kids... thankfully those things have lessened lately, and he has adapted well... but he's still a very very emotional dog.

We spend a lot of time with him daily, we have 5 acres for him to race on, the greyhound in him LOVES running! He loves the boys and must go everywhere with them, and sleeps on their beds. We love him a lot.

Anyways... with John and with Brenda he had doggy siblings. I believe that he is incredibly lonely. He is SO social when we take him to the dog park, I think he really wants a doggy friend. He's never been alone like that until our house. It is not an option for us to get another dog. At all.

We are building a new house, and at our new property we are within hearing distance of a gun range , on sunny weekends the guns are going off like a war zone, and we recently had Brody there and noticed how miserable he was... he was just an emotional wreck, and now we're worried about what life will be like there for him...

So, a few months ago Brody followed the car of our friends down our driveway and down the road about 1/2 mile, he stopped at a home that had 3 dogs in the front yard. They became BEST FRIENDS, and ever since then he runs away every chance he can get and goes straight there. He has even spent the night there, ON THE WOMAN's BED! The people there (three elderly folks) just love him, he is so happy there, when I go to pick him up he resists terribly. The other day they straight up asked if we would consider letting them adopt him.

I am so conflicted... he is obviously so happy there with THREE doggy friends, totally spoiled by the humans, 25 acres to run on... But we really love him a lot and I burst into tears everytime I think of letting him go. The kids could go either way on it, we've talked and they understand the situation, but get a little sad too...

Any advice would be appreciated... or just some listening ears... and prayers that we'd figure something out