Because you say that they have less throw, more pressure, and a longer duration before heads pop-up, it sounds like the length of the pipe from the house to the heads might be longer on your parents system than yours. Their net pressure to the heads could also be lower than your if they have more heads running from the same pipe from the house, in which case the higher flow rate is resulting in a greater pressure loss.
Then we might also be comparing apples to oranges (their heads might be ajusted to a different throw, they are using different heads resulting in different flow pattern and again a different pressue loss, etc).
