Choose any letters you want, but the parents must have the same first initials, the sons must have the same first initials, and the daughters must have the same first initials.
Middle names can have the same or different first letters.
SO1:
SO2:
(Feel free to add additional parents.)
DS/DS:
DD:
DS:
DD:
DD:
DS/DD/DD:
DS:
DS:
DD:
Pet: (Doesn't have to have a middle, but the first name should start with the same letter as either the parents or children.)