In the Bible there isn’t a genealogy of the Amorite King’s to determine their relations. We do have passages like
and all that he did to the Atwo kings of the Amorites, that were beyond the Jordan, to Sihon king of Heshbon, and to Og king of Bashan, who was at Ashtaroth. Joshua 9:10
Therefore we can conclude that both locations were of Amorite descent.
It would be reasonable to assume that a region had a king over them that was of their own nationality or from the same ancestor but just like the queen of England is German descent ruling over the British it’s possible to have a king not of the same descent. Much rarer in antiquity but not unheard of, for instance the Pharaoh at the time of Israel’s slavery in Egypt was an Assyrian ruling over Egypt.
For thus saith the Lord Jehovah, My people went down at the first into Egypt to sojourn there: and the Assyrian hath oppressed them without cause. Isaiah 52:4
In the event that the two kings were Amorites then at some point they would be related but how far removed is not something one can determine from the Bible alone.