All these threads about walking dogs in hot weather seem to invoke hyperbole about "wearing a fur coat"!
Having fur is not like "wearing a fur coat", any more than having hair is like wearing a wig. (Believe me, I have to wear a wig and it is hot hot hot, in a way that simply having hair is not not not.)
Unless you have acquired a dog that has the kind of heavy coat intended for sub-zero landscapes (in which case, why did you do that?), or you are failing to clip a dog whose coat needs appropriate clipping, it is very likely that your dog's coat is providing him/her with insulation against heat in summer, as well as against cold in winter.
This is why mammals in hot countries are not routinely bald. (Shout-out to elephants and rhinos, though. I'm sure they have their own, distinct, strategies of protection against heat.)
Us usual on these threads, there are also several horrified mentions o of dogs panting
! You might just as well be horrified by humans sweating.
Panting serves the same function for dogs that sweating does for humans. Both are a totally fine adaptation to heat, and are not, in themselves, a sign of distress.
I can't see in any of the OP's posts what breed her dog is, how old it is, what health problems it may have. So I'm assuming she feels that no dog should be walked at temps higher than around 20 degrees. I can't for the life of me think why this should apply to dogs in general, any more than it should apply to humans in general.
Unless the OP's dog is one of the unhealthy breeds, or is old or ill, I'm guessing that any temperature-and-activity combo that is comfortable for a couple in their 70s is comfy for the dog. If the OP doesn't trust them to make their own day-to-day commonsense judgements about the dog, it probably wasn't fair on them to ask them to take responsibility for it