Since you have 3 other siblings if you can afford it test all of them if they are willing. Test your parents if they are alive. Anyone in your grandparents generation, aunts uncles 1 st , 2nd cousins hit them all up if their willing to test. I have slowly been convincing more relatives to test but its hit or miss if the further back cousins on paper will match you on DNA. This is Family Finder test (like ancestry test) I am talking about.
again the % is really not going to help locate the ancestors no matter how many people you test in your family. If you test everyone its to find connections on relatives and missing links. My friend's mother was informally adopted. MT-DNA is Native American and as I said all the siblings show up with different AI %. They are not one step closer to finding their grandmother. To date no exact matches on MT-DNA full gnome and no cousin matches through autosomal testing. They are from the Canada/US border states. Most of the tribes in the US will not test as a whole but you may get lucky and some individual tribal members may test. We match a few from the US as cousins but it wont tell us if we share a European or AI ancestor. Again you need paper and or matching Y or MT-DNA lines.
You have a slight advantage with your lines being Spanish/AI at least at FTDNA since they have the biggest Mex project. I have a few very distant matches at FTDNA with Spanish names and none here at ancestry. They are too far back to connect paper trail. Our rerecords go dead quickly. Also the new Nat Geo project has gotten Mexico to participate in their study so this could be good for a lot of us who have ancestors that are west coast, SW and Mex area.