How does my mom make sure my older brother gets her house when she passes away?

that depends on a number of factors.  If this is the only asset in the estate it might be most efficient for your mother to leave a transfer on death deed to him.  However, that is a very limited deed and if he should pass before your mother it does not address a contingency plan.  If it is left to him in a will, it will mean that the estate has to go through probate court for your brother to recieve the house.  The gold standard is to leave it to him through a revocable trust.  This allows for contingent arrangements and avoids the whole court process.  Your mother of course needs other documents besides simply dealing with the deed.  She should see an estate planning attorney to review her whole situations.  Good luck to you.