Fallout New Vegas Faction Questions?

You cannot ally the BOS with the NCR, I tried to. You can ally the NCR, Great Khans, Kings, and Boomers. I took House out of the Picture and they all helped me in the final battle except for the BOS. It is your choice however. You can always use the fallout wiki the "The Vault" for help in a quest. You've got a long road before you hit the ending and you better pack some stims you'll need 'em.