Brother changed will 1 year before he committed suicide leaving…

Hello:
There is no automatic right to challenge the will. It can be contested, and it will be a question for the court as to whether the testator had proper capacity to make a will or not. The mere fact that someone changed long-standing instructions in one will to make new arrangements is not of itself sufficient grounds to set aside the new will. You will need to introduce some evidence to show that he was not able to appreciate his estate or appreciate making proper instructions at the time that he made the new will.
The old will would still need to be in existence, as it would then become valid if the new Will is set aside by a court. If all copies of that old will have been destroyed, then if there is no other pre-existing will , the intestate succession rules of Alberta would apply. Must provide.any spouse or children of the deceased, and parents have already died, then the siblings can inherit property.
Another option could be to sue the estate, based on the agreement with the brother that he was to have left property to nieces and nephews.
A lawyer is not mandatory for this but the law and procedure involved is not simple and an experienced lawyer will be very useful. We are not allowed to refer you to specific lawyers here due to site policies. But the Law Society of Alberta has a free referral service and they have information on that at their web site.
I hope this is helpful. If you have no further questions, please rate the answer positively, as otherwise the site does not credit me, even if you have paid a deposit. You can still ask follow up questions after rating though, if you wish.