Governance structure of Edom

I have noted that for Edom, there are Kings of various lineage aswell as Dukes of the lineage of Esau. How is it that both exist? Did they rule at the same time or was ist a shared/mixed system?

Gen36:

31  And theseH428 are the kingsH4428 thatH834 reignedH4427 in the landH776 of Edom,H123 beforeH6440 there reignedH4427 any kingH4428 over the childrenH1121 of Israel.H3478

32  And BelaH1106 the sonH1121 of BeorH1160 reignedH4427 in Edom:H123 and the nameH8034 of his cityH5892 was Dinhabah.H1838

33  And BelaH1106 died,H4191 and JobabH3103 the sonH1121 of ZerahH2226 of BozrahH4480 H1224 reignedH4427 in his stead.H8478

34  And JobabH3103 died,H4191 and HushamH2367 of the landH4480 H776 of TemaniH8489 reignedH4427 in his stead.H8478

35  And HushamH2367 died,H4191 and HadadH1908 the sonH1121 of Bedad,H911 who smoteH5221 (H853) MidianH4080 in the fieldH7704 of Moab,H4124 reignedH4427 in his stead:H8478 and the nameH8034 of his cityH5892 was Avith.H5762

36  And HadadH1908 died,H4191 and SamlahH8072 of MasrekahH4480 H4957 reignedH4427 in his stead.H8478

37  And SamlahH8072 died,H4191 and SaulH7586 of RehobothH4480 H7344 by the riverH5104 reignedH4427 in his stead.H8478

38  And SaulH7586 died,H4191 and BaalhananH1177 the sonH1121 of AchborH5907 reignedH4427 in his stead.H8478

39  And BaalhananH1177 the sonH1121 of AchborH5907 died,H4191 and HadarH1924 reignedH4427 in his stead:H8478 and the nameH8034 of his cityH5892 was Pau;H6464 and his wife'sH802 nameH8034 was Mehetabel,H4105 the daughterH1323 of Matred,H4308 the daughterH1323 of Mezahab.H4314

40  And theseH428 are the namesH8034 of the dukesH441 that came of Esau,H6215 according to their families,H4940 after their places,H4725 by their names;H8034 dukeH441 Timnah,H8555 dukeH441 Alvah,H5933 dukeH441 Jetheth,H3509

41  DukeH441 Aholibamah,H173 dukeH441 Elah,H425 dukeH441 Pinon,H6373

42  DukeH441 Kenaz,H7073 dukeH441 Teman,H8487 dukeH441 Mibzar,H4014

43  DukeH441 Magdiel,H4025 dukeH441 Iram:H5902 theseH428 be the dukesH441 of Edom,H123 according to their habitationsH4186 in the landH776 of their possession:H272 heH1931 is EsauH6215 the fatherH1 of the Edomites.H123

Who are the Kings and what did they do?

Bela

This is the son of Beor, the same person who is also the Father of Bileam who was the sorcerer that was hired to curse Yashrael during the exodus.

Jobab

This is the son of Zerah of Bozrah.

Gen36:13 And theseH428 are the sonsH1121 of Reuel;H7467 Nahath,H5184 and Zerah,H2226 Shammah,H8048 and Mizzah:H4199 theseH428 wereH1961 the sonsH1121 of BashemathH1315 Esau'sH6215 wife.H802

Gen36:17 And theseH428 are the sonsH1121 of ReuelH7467 Esau'sH6215 son;H1121 dukeH441 Nahath,H5184 dukeH441 Zerah,H2226 dukeH441 Shammah,H8048 dukeH441 Mizzah:H4199 theseH428 are the dukesH441 that came of ReuelH7467 in the landH776 of Edom;H123 theseH428 are the sonsH1121 of BashemathH1315 Esau'sH6215 wife.H802