You can make this soup with canned beans, but starting with dried beans is more traditional.
Soak navy and kidney beans together overnight (at least 6 hours). In another bowl, soak barley overnight. Two hours before making the soup, cook the navy and kidney beans in plain water 1 to 2 hours, until tender. Don’t precook barley. Set aside beans and barley.
Bring water and salt to a boil in a large stockpot. Meanwhile, prepare the kale. Strip leaves off stems and roughly chop. Add kale to boiling water along with the potatoes and split peas.
In a large skillet over medium heat, saute onions in olive oil until golden. Add them to the pot, reserving some of the oil in the skillet. Raise skillet heat to medium high and add beef. Sear beef until just browned, then add to the pot along with the linguica.
Add the precooked beans to the pot along with the barley and red pepper flakes. Lower heat and simmer 2 to 4 hours, until beef is tender and flavors have combined.