The Most Basic Rules
If citing multiple sources by the same author (or group of authors) with the same publication year, arrange the citations in order of title and place lowercase letters directly after the publication year in the citation:
Only use Arabic numerals (Vol. 3 even if listed as Vol. III), unless a Roman numeral is part of the title (Gasland, Part II).
If a source has no listed person(s) as author, look for a group author taking responsibility for the source and place the group author title in the position of author. A group author can be an institution, company, organization, etc.
If a source has no listed person(s) or group as author, move the title of the source into the author position. Only if a source is signed 'Anonymous' should anonymous be used in the place of the author.