Also concerning adding family member as a second guest, but let's be more specific:

Let's say A books the hotel and adds B as a second guest.

1) Can B check in and check out all alone? In other words, does A need to be at the hotel at any point during the stay?

2) A has no status but B does. Will B receive elite benefits (even though only as a second guest)?

3) B will pay for the accommodation upon check out. Does A still receive the night/stay credit?

Been mostly traveling by myself and first time facing such a situation. Obviously it can be YMMV depending on the individual hotel chains/regions/properties, but I'm just curious what's the common scenario based on your experience