My brother is staying in my moms house since she passed away in march. can he legally keep his siblings away from the home that was left to us all in her will?
depends. You should contact a probate attorney to properly file a Probate of your mother's estate and enter the will.
If your brother was given a quit claim deed prior to her death - then yes. If not, then NO. You need to file your mother's esate and enter the Will ASAP before all the assets are depleted.
Unless there is something giving him rights, the answer would be no. You are going to have to go to a probate attorney and have the matter researched. Then a course of action could be outlined on how to proceed.