Ok, I haven't played your demo yet, but as a few people have mentioned, your character development is really weak.
A friend of mine on another forum once came up with a great quote "No-one is truly evil". Although many RPG's contradict this, it's a great standing point to look at while developing your characters.
When I read about Roland and Erica, I immediately get a nagging 'WHY?' in my mind. Why exactly are they so determined to take over the other world? What's so good about it? Why is Roland draining Nina's energy instead of unimportant people he DIDN'T adopt? How come Nina stuck around for so long if she was getting abused in that way? Why is Erica corrupt?
I could go on, but yeah. You've probably got answers to all these questions in your mind, but unless you address them in either the storyline of the game or the character's bios, we're not going to know. It sometimes comes as odd that people can't see what you see, but remember, you're the one with the flash light into your story. Us, the players and the readers, are blind to the story, and you have to lead us through it, guiding us as if we were blind folded.
And with the war over the two different worlds, is there something wrong with the initial one? Why are they so desperate to escape their current one? Global Warming? Over population of monsters? It's up to you, but we need to know. Your story is very vague.
Also: Character Ages. Try to think of how old you are now, and estimate what you'll be like when you're their ages (I don't think you're older than your characters, except for the 7-year-old). If you don't see yourself doing what they do in your story, give them another 5 years or so. You may say 'Oh, but...my characters live in the medieval ages, they matured early then right?'
Very true, but mainly because the average life expectancy didn't go past 40 years old! Characters around 20-24 are pretty realistic. They're not going through puberty as an extra hassle, they don't have to worry about a lot of things. With the character you've given Nina, I'd make her a couple of years older. This means she's old enough to be able to properly take care of herself when she passes through to the other world, even if in a mediocre way. I'm nearly 16 myself, and knowing me and people my age, if the sort of thing that happens to Nina happens to me, I wouldn't go out on an epic quest to get revenge.
I'd probably have a mental breakdown, find an inn somewhere, get a job as a NPC waitress, and every night after stealing booze, I'd curl up in the stables next to a horse and cry my eyes out.
Now aside from that, your screenshots look pretty good, though they do come off as 'odd' in some parts. With your dialogue, remember the way a character ought to speak. Try to keep your sentences relatively well-structured, and don't just continue with the same paragraph on and on. Take breaks, take breathers, inserts some 'ums' and 'uhs'. It gives characters personality. Nobody knows exactly what they're going to say when they go into a conversation. No-one rehearses what they're going to say, so remember that. Think of how you might speak to a friend, where you might make up or completely fumble a word and come out with nonsense. This should be done sparingly, but it really gives characters more life, and makes the player think "I remember the other day when I did the same thing...". Relating to characters is what pulls players in.
Also, during dialogue, remember the characters age. Older people have broader vocabularies than young ones, unless they're very smart.
As another note in dialogue, I find the part where the young Nina and Xepher are talking annoying, to say at the least. He jumps from subject point to subject point without waiting for an answer. Between each sentence, Nina should jump in and say something, because that's the point of conversations. People can talk about the same thing for hours at a time! (Though don't do that in the game, because people like to repeat themselves).
Alright, I'm going to stop here. You have a decent game coming along here but it needs flesh and substance to really make it interesting. I hope you take nothing I said as an offense, I am just trying to help you.
Good luck with the rest of your project =D.