Can you contest your brothers will if he left everything to your sister?

Yes, you can contest your brother's will if you believe there are valid grounds, such as lack of capacity, undue influence, or improper execution. It may also depend on local laws regarding inheritance rights. However, the success of a contest depends on the specific circumstances surrounding the will and the evidence you can provide. Consulting with an attorney specializing in probate law would be advisable to assess your case.