Are my brother and I co-executors of my mother's will?

It seems that you and your brother are named co-executors of your mother's will. I say "seems" because I cannot give an absolutely certain answer to your question. Your mother's intention, as interpreted under the law of her state, controls how her will will be read. Still, the will uses the term "Executor(s)""”"”allowing for the naming of more than one executor. Plus the will uses "and" after naming your brother, and then lists you. By normal English usage, "and" means that both he and you are named as Executors. Unless there' some evidence that your mother intended to name only your bother as executor and you as alternate executor, or her state has some peculiar interpretation of executor will language, I think you are both executors.

The best solution here would be for you and your brother to agree that you are both named as Executors. If you do agree, it is very unlikely that a probate court would refuse to allow both of you to serve. [After your mother's death, her will must be filed in a probate court proceeding in the county where she lived.] If your bother won't agree that you can both serve as executors, you can challenge him on that in the probate proceeding. That challenge would require both you and your brother to spend money on lawyers' fees. This seems a waste, especially for your brother, who would probably lose.