i have thought about telling one of them to try taking over the DM reins for a while, but i thought the problem to be that they would lack the resources to actually design adventures for us - we are all poor university students, having zero store bought adventures, relying on free materials and my creativity for our campaign. as i am a bit more experienced regarding d&d (all of the group is completely new to tabletop gaming) i took the DM/adventure designer role happily, but i guess i could help them if they run into trouble by being a kind of co-designer, helping them make monsters/encounters and maps (i am the only one that has dundjinni). hopefully their lack of completely rules mastery wouldnt be disturbing at the table. definitely an idea to look at.
With all due respect, I'd suggest you don't have them take part in the planning. You have slayers and probably a bit of metagaming/tactical mastery going on from the players perspective. Removing the mystery won't push them towards immersion.
I doubt they are resisting RP out of a lack of respect or appreciation for what you are doing. I'd bet the opposite, or your original post would sound different and cite different problems. It's a bit uncomfortable to throw yourself in to those first attempts at "being" your character. In addition, college is just as much of a peer pressure situation as high school. Going out on a limb with heavy RP, or engaging with NPCs in a serious manner can feel like a risk, even in front of friends. I admit I don't know the players involved though, so take it for what it is worth.
Incorporating the RP in a more joking or bravado style (during encounters or not) may help them to work towards RP as a fun addition to their hack and slash adventures. I've found that even the most reticent role player can get in to certain RP aspects if they have a chance to find their voice in a way that fits their personality.
Give them some time and ease them in to it.