The two statements that are true regarding the issues and resolution are: the administrators are deploying their own change sets over each other, thus replacing entire page layouts in production, and a sandbox should be created to use as a unified testing environment instead of deploying change sets directly to production. Change sets are a way of deploying metadata changes from one Salesforce org to another, such as from a sandbox to a production org. Change sets can include page layouts, which define the layout and organization of fields, buttons, and related lists on a record detail or edit page. If the administrators are deploying their own change sets over each other, they may overwrite the page layouts that were previously deployed by another administrator, and cause the fields to disappear. To avoid this issue, the administrators should create a sandbox, which is a copy of the production org, and use it as a unified testing environment. The administrators can make their changes in the sandbox, test them, and then deploy them to the production org using change sets. This way, the administrators can ensure that the page layouts are consistent and complete in both the sandbox and the production org. Page layouts can be deployed via change sets, and this does not cause field-level security to be reset and fields to disappear. Field-level security controls the visibility and editability of fields for different profiles and permission sets, and it is not affected by deploying page layouts. The administrators are not deploying their own change sets, thus deleting each other's fields from the objects in production. Fields are not deleted by deploying change sets, unless the change set explicitly includes a field deletion component. Reference: [Change Sets], [Page Layouts], [Sandboxes]