The genealogy of this game is not short of amazing. I find really funny how Holmes is both half-brother to Attrom and cousin to Renee, who are at the same time adoptive brother and sister.
There are even a couple more ones if you think about it. Katri and Plum are also cousins (via Lionheart and Maria) and so are the three pegasus sisters to Katri (via Robert and King Dagnell). This last one is particularly amusing considering they are also cousins to Holmes through their mothers.
I'm pretty sure you're right about the first one. Don't know the answer to the second one, but they clearly knew each other well enough, they must had convived for an extented period of time.
I mean, as far as I know it's never stated if King Dagnell is the heir to the throne or just a consort. If Queen Maria was the one passing the Salia bloodline maybe a descendant of Plum/Lionheart could bear the brand of Yutona. And about Katri and Holmes: after the desert chapter in Berwick Saga, Tianna talks about a very old story her grandfather told her about a blond treasure hunter and his consort, which would tie well with the ending of TRS. Take this with a grain of salt, of course.