Hi Adam,
I will admit it has been a bit since I've done this myself but it is possible to move over two related tables and maintain their relationship using an option under App Management labeled "Move a table into this app". What that does is allow you to pull in a table from another app, when you do so you are given a warning that any relationships might be broken by moving and they will until you move in both the child and parent table in the relationship, then the relationship knits back together. I recommend moving the parent and then the child table. The one side effect to this is since the parent comes over first any report link fields break but they can be recreated by editing the field properties and just reselecting the reference field in the child table to line them back up and get those reports to populate again once they are both moved over. Your existing reference fields and summary fields do come over. Then you would update your existing roles to decide what their permissions would be on these new tables (by default they are none).
There is one thing that can throw off this setup though, if the tables you are bringing in are the same name and set up as as any tables in your existing app the child might relate to the original table over the table you brought in. For examples if both of my apps have the exact same Projects and Tasks table becauseI used an app from the Exchange for both and then I move them over my new Tasks table might grab onto my old Tasks table, but that is an odd outlier that requires such a set up. I hope this information is helpful.
