Just thinking aloud in case someone notices some of this and saves me from answering this question.
Three of them (Meneldil, Eorl, Théoden) came to rule when their fathers were already dead. Meneldil was "given" the rulership by his uncle, while Rómendacil also inherited the kingdom by the same sort of a jump. Théoden "did" this to Éomer. Both Meneldil and Rómendacil were supposed to be regents or stewards at first. The three of them except Théoden (if Meneldil was in the War of Last Alliance, which he probably was) also fought some important battle before they inherited the kingdom. Three of them except Meneldil died in battle. All of this are sort of "what do they have in common"-like things, though, and also it is all quite crooky (it's always one character missing or it's somewhat switched).
I also tried to make out some mathematical dependance between them, like for example if the second was always two times older or ten years older than the first when he inherited the throne, or died, or whatever, but Eorl was in general younger than Théoden and it doesn't work.