So, back to the example of the two men (lets call them John and James) we think might be brothers: We find two g-g-grandsons (or any male descendant in a direct father-son line) of each, preferably the most distant cousins we can find, and get a Y-DNA test done for all four men. Usually a 37 marker Y-DNA test is a good place to start. This looks at 37 sections of each persons DNA that the genetic scientists think are most useful for our purposes (the bits that are least likely to randomly change over generations). The results come back looking like a fairly meaningless string of numbers which are fairly useless on their own, but allow us to compare each persons result with others in the database of the testing company.
The most important part of this process is registering your kit before shipping it. All five services require this, and if you don't do it, you won't be able to access your results. This requirement is to protect your privacy—your name won't appear on the kit or the results—and to easily track your kit as it goes through the process. Of course, when you sign up for an account with these services, your identity will be associated with it, but the sample and any reports stored on the service's end will just have a unique barcode.
I’m afraid that you're unlikely to find a DNA test that can tell you specifically which tribe your ancestors came from. We’d recommend taking a look at the answer to this forum post, which explains a bit more about why this is the case: https://dnatestingchoice.com/forum/showthread.php?1259-Welsh-Ancestry. Although the original post was about Welsh ancestry, the concepts are the same regardless of where in the world the specific groups of people lived.
Every company on this list promises test results in 6-8 weeks after they receive a sample, except for MyHeritage DNA which claims 3-4 weeks. This can vary however and is influenced by demand and other factors. It is generally a good rule of thumb to anticipate that it will take 2-3 months for results once you order a test. This accounts for the time it takes for you (or your recipient) to receive the test, provide a sample, mail it back and for processing of your results.
Both men and women can take mitochondrial DNA tests (because we all possess mitochondria in our cells), but it’s worth noting that women are unable to take Y DNA tests as they do not possess a Y chromosome. If you’re female and you’d like to learn more about your paternal lineage, you can ask a close male relative to take a Y DNA test on your behalf – read our article about Y DNA testing for more information.
Autosomal DNA Tests: These type of tests have become extremely popular over the last couple of years as prices have dropped and the amount and accuracy of the results has increased. Autosomal testing looks at information across the genome to provide clues to our personal ancestral history on a much broader scale than either mtDNA or Y-DNA testing can. While this type of genetic testing is an ever evolving science, you can expect to get a general breakdown of your ancestors’ geographical origins (your admixture) as well as connections with people who share your ancestry. This can be a unique and exciting way to tear down those brick walls and uncover branches of your family tree you never knew you had. For some, the results can be surprising and enlightening–for others, there can be a simple verification of already known information and even some disappointment in discovering nothing new.