Lissa and Henry's relationship could be considered to mainly be based on sex, since Henry wanted to marry her since she was "nice and warm" because they slept, not like that, so they would eventually fall asleep. I'm sure when they got married it would've got adventurous and thus is Owain, but look at his personality, we can all agree there's something wrong with Henry, but that's why we all love him, why do you think Owain might shout out random things? It's a little weird, Henry can say weird things and Lissa can be very loud so in terms of personality it actually works quite well I think.
Let me know if I've missed something or you want to contradict me. But this is my full theory and I hope you enjoyed. I might make a whole video on it because I'm on summer holidays... Depends though.
Thanks for reading.
Dr_Emblem