Answers
What happens if I make changes on my iPad and on my Mac?
Changes can be made to the same family file on the iPad and the Macintosh simultaneously. In fact, you could place your family file on multiple iPads or iPhones, make changes on each device and on the Macintosh, and then send the changes back to the original family file on the Macintosh.
For example: You might add 10 new people on the iPad and edit data for 5 people and then add 10 other people on the Macintosh and edit 2 more people. When you send the changes from the iPad back to the Mac, all 20 new people and 7 edits will appear on the Mac. At this point you would want to send the updated "master" family file (on the Mac) back onto the iPad.
Note: changes could be lost if the same data has been edited on two different systems. I.e., you should avoid making changes to the same fields for the same person on different systems.