They are known as the Earl and Countess
The word Earl mean knight so the Earl or Durham is the Knight of Durham
Step father and son
No. The eldest son of an Earl usually takes on one of his father's lesser titles: for instance say the Earl of X also has the titles Viscount Y and Baron Z. The Earl's son is thus known as Viscount Y. If Viscount Y has a son in his father's lifetime, that son, the Earl's grandson becomes known as Baron Z. Note that these titles are courtesy titles, and are not official. The Earl of X's son may be known as Viscount Y, but the official Viscount Y is still the Earl himself. Note also that in some cases an Earl will not have any lesser subsidiary titles (i.e. the Earl Temple of Stowe). In such a case, the Earl's son and heir will be given a made-up title (the Earl Temple's son is known as Lord Langton, a title that does not legally exist). These same rules apply to Dukes and Marquesses, but not to Viscounts or Barons: sons of Viscounts and Barons are not entitled to courtesy titles.
In the British nobility, a viscount is ranked immediately above a baron and immediately below an earl. I doubt whether a viscount would "serve under an earl" as you put it.
Matthew Earl Thompson is 5' 10 1/2".
Brother of James Earl Jones.
Jerald Sowell's birth name is Jerald Monye Sowell.
Jerald Sowell is 6'.
Jerald Jay Savage's birth name is Jerald JaVon Savage.
Jerald Honeycutt was born in 1974.
Jerald terHorst was born in 1922.
Jerald terHorst died in 2010.
Jerald Johnson was born in 1927.
Jerald Olp is 5' 9".
Jerald Garner is 5' 9".
Jerald Clark was born on 1963-08-10.