Such a sad story and ending, but Family has to come first, if one of your youngsters had got in the way you would never have forgiven yourself,
Most of our dogs have been rescue dogs of one sort or another, some we had to give up on but they weren't nasty so we found good homes to suit their problems, but you always wonder what gave them those problems in the first place, though the beautiful BC who fell over backwards in terror when I picked a brush up said it all :-(.
Another would suddenly turn, once he was REALLY snarling within an inch of my inner thigh, his eyes were just crazy, thought I was a gonner there, but I cried when he had to be PTS, he'd started have nose bleeds when he got excited/barking, vet said he was too old to operate on.
You gave Dingo a chance, sadly somethig was wrong in there and it didn't work out, well done for trying and giving him chance after chance.