They can't be, at least not for "perjury", because "under penalty of perjury" has no force unless authorized by a court or, I guess, some specific statute.
The idea that you can stick the words "under penalty of perjury" on a random form to create a legal requirement for truthful answers is one of those Internet legal old-wives-tales, like adding "no copyright intended" to a Youtube upload.
However, if you report that someone else is dead, and they or their family suffer harm as a result, you can probably be sued easily, regardless of whether you use Facebook to make the report, or a carrier pigeon.
Not just while testifying in court. Statutes can also require declarations to be made under penalty of perjury. Valid DMCA notices, for example, must contain one.
The idea that you can stick the words "under penalty of perjury" on a random form to create a legal requirement for truthful answers is one of those Internet legal old-wives-tales, like adding "no copyright intended" to a Youtube upload.
However, if you report that someone else is dead, and they or their family suffer harm as a result, you can probably be sued easily, regardless of whether you use Facebook to make the report, or a carrier pigeon.