Looking for guidance regarding Guardianship / Conservatory.

Deemom154, based on your father being your 74-year-old mother's caregiver, it seems probable that a guardianship judge will not appoint a guardian or conservator for your mother because neither of those appointments are necessary when there is a capable spouse already de facto serving in those capacities. If your father is actually not "capable," then perhaps he needs a guardian, as well, and he shouldn't be your mother's caregiver.

But, to answer your questions, some states, but maybe not all, allow but discourage multiple guardians and/or conservators. Also, each state's laws specify the authorities given to guardians and conservators, e.g. "whether a guardian can spend small amounts of money." The guardianship court in the county where your mom lives probably has on-line information that describes who needs guardianship/conservatorship, who can be guardian/conservator, and what the duties and restrictions are. And your state's Bar Association may have on-line information, e.g. here's a link to the Idaho Bar Association's Guide: https://isb.idaho.gov/wp-content/uploads/bro_guardianship.pdf

I have multiple experiences with guardianship and conservatorship in situations where they were a necessity, and I advise petitioning courts for those formal authorities and responsibilities only where there is no other way to ensure the well-being of another person. If you haven't discussed your and your brother's plan with your father, please do that before you do anything else. Whether or not to discuss this with your mother depends on her cognitive level.

Your answer has nothing to do with my questions.
To answer your question, my mother has serve dementia and my father is her caregiver

How does your mother feel about this? And what's the basis for this decision? For what reasons do you feel she needs a guardian and a conservator?