Spelling Rules -- Making Noun Plurals - Page 3

Rule 8: The plurals of single capital letters, acronyms and Arabic numerals (1, 2, 3,) take an 's' without an apostrophe:
  1. Z (the capital letter Z) --- Zs
  2. POS (Point Of Sale) --- POSs
  3. ATM (Automatic Teller Machine) --- ATMs
  4. 7 (the Arabic numeral 7) --- 7s
Rule 9: Of course you cannot make a plural of an uncountable noun. Some examples are:
  1. information
  2. blood
  3. paint
  4. harm
  5. cattle
Rule 10: Some nouns by a quirk of fate exist only in the plural. Some examples are:
  1. pajamas
  2. scissors
  3. spectcles
Rule 11: Some nouns by a quirk of fate exist only in pairs. Some examples are:
  1. a pair of scissors
  2. a pair of pants
Rule 12: Some nouns by a quirk of fate are the same for singular and plural. Some examples are:
  1. deer
  2. sheep
Rule 13: Some nouns by a quirk of fate appear as sigular and plural but are actually separate words. Some examples are:
  1. due - dues
  2. spectacle - spectacles
Rule 14: Some nouns exist both as pairs and without pairs.Some examples are:
  1. glasses (eye glasses) - pair of glasses
  2. spectacles (eye glasses) - pair of spectacles
Question: Some people refer to their children as a pair of twins.

If twins are two people is a pair of twins four people? And those with two pairs of twins 8 people?