You can use a conditional value list for your radio buttons, but care will be needed. Unlike drop down lists and pop up menus, the values from the conditional value list must fit within the borders of your field. If your conditional value list has more values that will fit, a values may be missing or only partially displayed.
Here are some links on conditional value lists:
There's a lot of overlap between the first two links so you can read one and skim the other. The demo file gives you several examples of different conditional value lists so you can examine them to see how they are set up. If you are using FileMaker 12, you can open this demo file from your File menu to get a converted copy of the demo file that you can examine in FileMaker 12.
The last link discusses how to set up a chain of conditional value lists where the value selected in each conditional value list controls the values listed in the next value list.
Forum Tutorial: Custom Value List?
Knowledgebase article: http://help.filemaker.com/app/answers/detail/a_id/5833/kw/conditional%20value%20list
Hierarchical Conditional Value lists: Conditional Value List Question
Feel free to post follow up questions here if those links aren't enough to get your radio buttons working correctly.
Thank you! The realtionships weren't my issue but I certainly saw in your demo file that I had initally misunderstood how certain condtional value lists worked. Much appreciated!