Especially when you consider that Elves, and Elven hybrids, live longer than humans. So if you put an Elven hybrid into the line of succession, even coming from a third princess, there's a chance that, as Aimery kings and queens who only live 80 years die out, an Asuvian monarch with Elven blood could ascend to that throne. They're as tricky as any royal family!
Yes! They both gave their consent to it and are going to do their best to make it work. We'll just have to see what happens. :D