We have had Pyrenees for over 20 years, both pups and rescue dogs. With 7.5 acres the dogs will claim the entire place as their territory. No worries about them bonding to the kids and the livestock. They will do both very well. I watched your video. Eventually, the dogs will attempt to dig out under that
fence. If the ground gets soft when wet they will succeed. An 18" strip of
chicken wire flat on the ground secured to the bottom of the
fence and tacked down will keep them in. Pyrs have a large territory. Maremmas - the Italian model of the Pyrs - have a much smaller territory. This results from the two different ways the dogs are used in their home countries. The pyrs stay out in the mountains with the flock. The Maremmas come back to an enclosure at night and stay there with the flock. This results from the extensive use of sheep for
dairy purposes in Italy. We have a Maremma and a Pyr now. The Pyr is the one to always test the fences.
Also, if getting pups, early personality tests can be done to determine the best type of environment/use for the pup.
Rescue dogs are, of course, more of a gamble. Molly a rescue Pyr that we had in Montana was extremely aggressive to predators (including strange dogs) but mild and sweet to kids and human visitors. She ran off a grizzly sow and cub one night and a very large black bear a few weeks later. All our neighbors had cougar trouble - but we never lost a sheep or goat to a big cat there. She was a wonderful dog. We have had other rescues who were a bit ditsy.
Much good information is available in the book Livestock Protection Dogs by Sims and Dawydiak.
Best of luck on your homestead.