let’s not forget there were numerous tethers that just untethered themselves for no apparent reason
Yes, i’m not quite clear on that though. Is their story that the tethers were supposed to be tied but someone forgot to tie them (or didn’t tie them properly) and that is why the father was yelling and cursing after it flew away? Whatever the story might be, it makes no sense for the father not to have checked the tethers to make sure everything was set up correctly before the big experiment.
Upon further reflection i should amend something i wrote earlier. If it turns out the older brother’s story is that the younger brother crawled into the balloon earlier in the day, then perhaps it could be argued he wasn’t lying to the police, he just didn’t realize that Falcon had left the balloon and went up to the attic to hide. Thus that could be said to what led to the parents not searching the house thoroughly, for they believed their son when he said that Falcon had been in the balloon.
Having conceded those points i still don’t believe the story is any more likely, only that the script they were following was not as amateurish as it first seemed to be.