I actually like your idea! Plus it’s shown that none of them are dating, and that Herman rejected getting married- they could both be the uncles.
I could imagine Herman coming more and more to the estate, as he’s slowly leaving his role of Duke behind and wants the pressure of his parents and family expectations off his back. At first he has a kind of rivalry with Ulrich, “competing” for their nieces/nephew’s attention and to spend time with Anissa, but the more they do this, the more they enjoy each other’s presence and they end up sympathizing also with what they went through in the past, due to the war of roses that was meant to happen and the rivalry between their family. I would’ve loved for that to happen, but sadly, reincarnation stories are often very straight (I was so surprised to see Veronica dating another girl, even if she had that girl boss vibes).
Since we know that Veronica dated Sara for a while she must be a lesbian or bisexual right. Well, I kind of want Herman and Ulrich/Yurik to date/become a couple.
Anyways I like the plot and storyline hahahaha. And I like that the author didn't make it sound like the demon suddenly became kind because demons will never be kind. And that Baal only sided with D and A because they are stronger. And also about Helios.......etc.