The Curse of Lanval Series. The Curse of Lanval, #1

Book 1: MirrorsThe greatest adventure of my life started with a discovery in a history book by my sister, Jules. Don't let anyone fool you, this truly is all her fault. Well, not my Uncle Richard's death, but everything else. Now we are stuck in 1154 A. D. and it's all her fault. Book 2: MarieThis book is all about her, me, us. My lady in red. What I am braving right now as I head to England to become King Henry, with a wife who hates me, bandits in the wrong time period, and more ale than I can handle.
Yeah, still stuck in the past, and it sucks. Book 3: MagicI can't wait until we get to the Cliffs of Dover. I've always loved England and wondered what it looked like in the twelfth century. But first there is something I have to take care of. The queen still hates me, and now Jules is always missing too. I swear I've lost my mind, drunk too much, or Medieval France is finally getting to me. I don't miss anything from the future.
Well, I miss Mom. Book 4: MerlinThis is the end of my story, of this story. It's about how I die, don't die, save the kingdom, get the girl, don't get the girl, all your typical hero stuff in one book. And the most epic battle, with the most famous sword in history. and oh, it's totally my fault this time.