I am close to someone who has a 100% British heritage and is yet is a Status Indian. There is a long and convoluted tale that involved a lot of issues including an acceptance process with the band elders. I imagine that another band (or this band at another time) would make a different decision. The point being that asking for a flow chart of rules ignores the inability to translate easily the rules into our black and white semantics, ignores the consensus nature of how these decisions are made, and ignores the different cultures that exist in Indigenous communities.
If you truly need to know. Speak to people in the community - though they may not be interested in educating you.