Let's look at this another way.
If the baby carrier was indeed a Kangaroo, (not the sling kind), one parent had the baby, in front. Not a back carrier. A front one.
Let's look at intention, not outcome.
Now we know they started early.....
How long ought that trail take? Anyone know?
Is it reasonable to think they planned to start early and finish before hell breathed on the earth?
If they got a later start, even if only by a half hour or an hour, what a vital difference that could have made!
So let's put them an hour behind schedule.
Mom, Dad with baby, dog.
They were found a mile and a half from their vehicle. What's a reasonable length of time, given favorable conditions, to hike that distance?
Remember that late start (JMO).... they were so very close to completing their hike! Even with whatever chain of events they were enduring, if they'd had lower temperatures longer, they might've made it out!
If we assume the dog was unleashed (seems to be their habit), it's reasonable to assume the dog might run ahead, run askance, make its own trail... and hot and thirsty, find water. Algae infested water.... (it's also possible as someone suggested upthread that the dog got separated from them and they had to spend considerable time looking -- while the mercury climbed -- even hot, too hot, who could turn back and just leave the pup to die?)....
My theory is that the dog is in distress first.... whether by algae or heat. And a decision is made (never once thinking the decision, not only wouldn't save the dog, it would prove deadly for everyone) -- to carry the dog.
Still JMO, mom takes the baby -- by now, they are all hot, thirsty...
Dad carries the dog.... and now they're hurrying... which only increases the exertion... the temperature keeps climbing, the dog is failing.... and dad is way overheated too.... the dog becomes lifeless.... dad sits, says he needs just a minute. But it's clear he's not getting back up. Mom has to get help. Or at least to somewhere with cell coverage. She can go faster alone. So dad becomes a tree, providing the only shade they can for baby.
She tries to hurry to get help.... but she succumbs to the heat....
If they did get an earlier start, if just that singular variable changed, could this have had a better ending?
How I wish this could've been a feel good story, where mom and dad and baby brave the mountain to save the family dog! IMO they were 1.5 miles from that happy ending...
Nothing nefarious. Just a tragic combination of events which pitted them on the trail longer than they planned IMO facing scorching temperatures, compounded by a stifling haze...
They may have died, trying to save their dog...
JMO
All so very sad....