Since it appears from your question that your mother left a written will, then it needs to be probated. As to the question of whether your brother can change anything in the will, the answer is generally no. Once the probate starts, and if the conditions require it, the court may allow certain changes to occur (such as sale of property meet debts of the estate). However, the wishes of your mother can not be changed at the whim of the executor. If he does, then he is violating his fiduciary duty.
To see if the process has begun, you should check with the court in the county which your mother lived. That is where the probate should occur. However, an even better place to start would be talking to your brother. If he is the executor, you will find things out faster with the added bonus that it does not escalate any potential problems.
If that does not work, or you think that something is going wrong with the estate, (for example that executor is refusing to start the process) you should consult an attorney as to what your options are. However, keep in mind, probate are not quit. They tend to last at a minimum 6 months and can go on longer depending on the complexity of the estate.
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