My sister owns her house. My brother lives with her. If she would die. Does he automatically get the house?

No, living in the house gives him no additional rights to ownership after the owner dies.  Assuming no major creditors of you sister's estate (which could be you if you claim that you are owed something for the work you did on the house), ownership of the house would pass pursuant to her will.  If no will, it would pass by the laws of intestacy.  I am not familiar with the Pennsylvania intestacy statutes, but they likely provide that, if there are no surviving children or grandchildren (or parents) it owuld be divided equally between the surviving siblings.