Mandie I am sorry to hear your friend has lost one dog due to old age and that the other is now has Parvo....If the dog does have Parvo the vet should have quarantined him/her, and began I.V. treatments and other med's used. I have dealt with 2 puppies in the past that had parvo, and sadly one wasn't diagonosed fast enough and passed away in my arms, as for the other we were lucky enough to know the signs by then and was able to seek treatment for the dog.
We had a big scare here in Feb/March when Beau & Ajax were showing severe signs of Parvo and here they don't quarantine like they do in the states, so we had them on I.V. fluids, meds, and injections at home although it turned out not to be parvo the initial med's did help whatever virus they had. Sadly Parvo can be brought in on your shoes as well, if one walk's through an area that has the live parvo virus, such as grass for example they can track it into their home. Yes proper vaccinations do help however keep in mind that even when vaccinated a puppy under the age of 6 months is still said to be at a high risk, and then of course the risk get's lower from 6-12 months, however it is known that a dog can get the parvo virus up to the age of 2 and it is not common (but not unheard of) for a dog over 2 to get the virus.
This is just from my personal research and dealings with Parvo and working in a vet clinic many many years ago. The research you have provided above is excellent and I think everyone should read it. If your friend's dog does have Parvo I pray they are treating it with the proper med's and that they have dissenfected their house from top to bottom with a 10-90 bleach/water solution, you (they) can even use that solution in a spray bottle for furniture, carpets, drapes, ect. As it isn't strong enough to bleach any fabrics (but still take precautions). You (they) can also take that solution and place it in either a very large spray bottle or buy one of those yard sprayers for the lawn and spray the grass and outside surrounding areas with it as well. Parvo is a nasty disease to clean up after, but if all precautions are taken all should be okay. It is also uncommon for a dog to get Parvo twice from my understanding, (but I could be wrong).
I hope all works out for everyone