This is a personal decision, but we recommend naming 3-5 trusted people as guardians of your children and each of the other roles. You will choose one person as the primary candidate and others as backups (arranged left to right in order or priority). If your primary guardian is unable to fulfill the responsibility, the backup would step into the role (subject to court approval).
Remember, you can add people to a role and arrange the order at any time. If you happen to change the guardian or executor, be sure to update and execute a new version of your will.