I am the main caregiver and live near mum. I have a brother and sister. I think all 3 of us should have enduring guardianship. But I am worried about what would happen if my brother or sister want my mother in a nursing home near them and too far from me and don't even visit. I would want to visit at least a few times a week.
In any case, I second CW's point. Sharing and consultation are great, but in the end it's impractical to split guardianship effectively three ways - it just makes the whole job pointlessly complicated.
Would your brother and sister have a problem if you were your mother's guardian?
Also, where are you? Different countries have different rules for guardianship.