In all my months and months and three years of gaming, I can say that no matter what a GM does, how they do it, whatever tactics or whatever they use, if a person does not want to roleplay, they won't roleplay, period. Nothing a GM can do will help them, or cause them, to roleplay (and I mean getting into characters, thinking like their characters, that kind of stuff).
I tell everybody that I play with, when I run a game, that the more they put into the game, the more they put into their characters, the more they will, in turn, get out of the game. If all a person does is roll dice, pick a race, class, equipment, and say they are ready and then only act like they want to fight, and then later they say they are bored while the two others who made up some kind of background and speaking to each other in character are having more fun, then as GM this situation would not be my fault at all. It would be the player's, and this player would have chosen to not put as much into their character as the other players did.
It's not just up to the GM, its up to the players also. Sometimes things outside gaming come up, like a split up in a relationship, and if that occurs its better to play video games where you can kill things (like Soul Caliber 2, Tekken, things like that) are better alternatives than to roleplay.
But, I think some players also expect the GM to provide everything for them, and those players won't get as much out of the game due to this miss-expectation.
Create a campaign environment that encourages roleplaying. Create adventure situations that require something more than hack-and-slash to accomplish - perhaps the PCs need to convince someone to do something, or maybe they need to investigate something by asking a lot of people questions. Make your NPCs memorable by using distinct voices, postures, and attitudes for each one. If an NPC is entertaining, the players will want to interact with him. Ham it up, and don't get embarrassed. Finally, make the players aware that they'll get extra XP for good roleplaying.
One question you might also want to ask yourself is if you punish your players for roleplaying.
If they develope relationships with NPCs, do those NPCs suddenly start getting kidnapped and threatened at every turn? Each time they put some trust in an NPC they have been dealing with, does that NPC betray them? If they help a community, does the community welcome them or still try and cheat them out of every coin they can?
I remember finding out in one campaign that I was the only character with any family ties. I found this out after an adventure that started out as a bethrothal celebration for my character's sister. There were over 30 deaths before we took out the vampire that has shown up, and never did catch the murderer.
The other players mentioned that fear of something like this happening was why none of them had defined family or friends in their background.
Make sure you aren't teaching the players all the wrong lessons when they do attempt to roleplay.
Personally I would just go along with the group's preferred playing style. By the sound of it they would read CE to alignment-detection, and should be wanted for murder, theft et al in most places. I'd let them be hunted renegades and see how it feels to have high-level NPC adventurer parties out to kill them and nick their stuff. I don't believe in forcing players to act lawful, or good, or whatever to fit with my plans - I give them a world to play in, potential patrons, enemies etc. My last group basically 'went evil' due to a money argument with a patron and ended the game as hunted renegades, the current group seem to be more into working with the local authority figures and are building their reputations as 'good guy' heroes. I enjoyed GMing both games.
One question that crops up into my mind when seeing the diverse racial types of your player's characters is where are the parents? Half Dragon? Celestial? These beings have ties to other places and even other planes and it might make for some good opportunities to add those elements into the game.
On the other hand, there is nothing wrong with an action adventure style RPG and if the players are having fun, run wild with it.
There are other ways to incorporate role playing. Some of them requiring some campaign altering decesions. Instead of thinking big foe that they can't beat, try big foe that beats them, strips them of their items, and puts them in a prison plane where they can only navigate from place to place by helping those in power here as they play off once another trying to gather power.