"I still don't think they're related at all. There hasn't really been convincing evidence that they are, mostly just people assuming they might be because they are in the myths. Nothing that's actually come up in the episodes has said Arthur and Morgause are related, or even really implied it. *shrug* Or at least that's how it seems to me.

Morgause did get the bracelet from her mother, but that doesn't mean that her mother is the one she's related to Morgana through. Like you said, the bracelet was probably a gift from Gorlois. And why would the mother give Morgause a gift symbolizing a house that Morgause wasn't technically a part of (if she was Uther's daughter then she would belong to the Pendragon dynasty, same goes for any other man she might've had Morgause with)? It would be like a mockery to give her Gorlois' crest when she wasn't actually Gorlois' daughter.

In fact, if Morgause knew her mother when she was growing up, in exile, doesn't it imply that her mother was someone who WASN'T in Camelot? As in, not Ygraine because Ygraine was married to Uther, and not Morgana's mother because she was married to Gorlois and having Morgana? Otherwise how would they even have known each other?"