I always wondered about that. DC can ask Rica if she's going to be queen, and she'll say no, she's just a concubine. She says Bhelen's wife will be queen. And if you ask Bhelen if your nephew will be king, he'll say that baby Endrin has just as much a right to the throne as any child born of his wife.
Then the crier says the "marry a casteless" thing, which could just be ~scandelous rumor mongering~ and Anora will address Rica as Bhelen's wife in the epilogue (could be a cultural misunderstanding or design oversight?), and if you side with Harrowmont eventually Rica will say something like she's glad she doesn't have a husband to boss her around.
At any rate, I kind of like the idea that he's genuine in this one thing, and would like to marry her. But I honestly don't know if he did or not.
It's probably something like a cultural misunderstanding and poor translation. Rica may consider Bhelan her husband for lack of a better word in Fereldan.
As for little Endrin, that's why the nobles take many concubines. They have a low birth rate, so a noble, considered better by dwarven custom, having multiple women makes for multiple superior children, or so dwarven social custom dictates.
I did a script on the banter thread once about the dwarf warden and Anora getting into it about this. I headcanon that my dwarf girls consider themselves Alistair's noble-hunter, and so frequently argue with Anora over whether any of Alistair/Warden's children deserve the same upbringing as any child of Alistair/Anora. It ends with Alistair being revealed to be hiding under a table, and asking the inquisitor not to tell them where he's at. 
By the way, did anyone find the letter in the Hinterlands addressed to Endrin? I wondered if that was Bhelan and Rica's child, since he's born before the warden makes the decision, and therefore likely lives in all playthroughs. But he's about Kieran's age, so....