This story from the NYTimes is an up-close look at an issue that is becoming more and more relevant for many tribal nations - namely who has a legitimate claim to tribal citizenship.  Per capita dividend payments from successful tribal enterprises has given new meaning to this question recently.

https://www.nytimes.com/2017/01/18/magazine/who-decides-who-counts-as-native-american.html

The story is about a NW tribe, the Nooksack.  If you want to learn about enrollment rules for the Tohono O'odham Nation, you can find a marked-up document that represents proposed changes to their Enrollment Ordinance here:

http://www.tolc-nsn.org/docs/EnrollmentAmendments2016.pdf

The Nation recently sponsored a series of public hearings on these proposed changes.