Realms are the keys that need to be selected exclusively, with some options disabled as the process goes on.
In terms of form elements, this can be either checkboxes or radio buttons:
By using form elements with documented altered behaviour, the system is further fragmented and becomes more testable.
By using existing constructs, the redundancy increases assuming an intelligent user or tester who is able to use the underlying concept (i.e., realm names next to form inputs in place of actual icons). This also reduces the base need for overkill graphics for development/prototype cycle.
Checkboxes allow for selection and being disabled; on top of not having key navigation. However, they allow for multiple inputs at once.
Allow for only one to be selected at a time, which means that if a selection is locked, there can only be one selection. Meanwhile, they can be keyboard navigated (also there is no native click event) which makes the usage confusing. The only two real benefits are - natively exclusive and no deselection.