You and your husband were very new to the US and specifically to the local coyote threat in the high desert of California. While some mentioned the existence of coyotes to you, I really doubt they adequately conveyed the dangers involved to you if you took your cat outside.
My point is that while I do understand you and your husband feel guilt, and it is a really difficult and painful emotion for you both to deal with now, but when you can be and are being fair and realistically honest with yourselves, and not purely emotional, you did not understand or really know the threat involved. If you did, you would not have taken your beloved Dolly outside into the fenced in backyard as you were doing. I am urging you to try to release the guilt you are feeling over time, as you go forward, because the guilt is not fair to you. You loved Dolly dearly and you always protected her. What occurred, in my opinion, was out of your control.
I saw wild coyotes in Joshua Tree National Park multiple times on probably 3 visits there. That was California high desert country. Those coyotes were NOT afraid of me and my wife. I was and am 6'1" and 200 pounds, and very fit. A few of them walked up to us, much closer than I wanted them to, because some idiot park visitors obviously had been feeding them on occaision. I was ready to kick them to the best of my ability if they came any closer. These were probably 30 pound coyotes. There were in control of the situation; I was a visitor and they knew it, and they were on their home turf.
One of my main points I am trying to make is that coyotes quickly loose their fear of humans after they have positive or successful encounters with us. When humans feed them. When they come to our houses/neighborhoods and run off with our small pet dogs and cats.
I am sorry, but these 3 you husband encountered after he jumped the fence were probably not afraid of him for these reasons. They are fast, much faster than your husband, and unless he was very close to them, they knew they could move or run away from him. As they did.
Your wrote that understanding all of what happened is important to you, including the behaviors and actions of the coyotes, so you can make sense out of it in your head.
In most of America today, in my observation and understanding, most cat owners keep them inside always. 20 to 40 years ago it was the opposite. But today is very different. Coyotes and other wild predators are real threat, large domestic dogs, cars, and more...
I worried about my Tasha whenever I took her out on the leash in the neighborhoods we lived in. Some were very nice HOA communities. Tasha was muscular and 60 pounds; and she was not shy about protecting herself. But in some of the neighborhoods there were loose aggressive pit bulls much bigger than her and loose aggressive rottweilers who were twice her weight. I carried a spray canister of "dog repellent" almost every time I walked her, so I could protect her. We had encounters and I called the police a number of times, dialing 911, as these large dogs were equally a threat to me and my wife as I held Tasha's leash. My point is probably that when we in the US are very aware and very educated of the dangers involved in protecting our pets, with something as simple as walking your dog in a very nice upscale HOA, you are always in danger with your pet outside the safety of your home.
Morgan, my wife and I send you our deepest condolences. This should never happen to anyone, to any cat owner. We are thinking of you both these days.