I'd recommend you look into the Click'r range of Shimano. The pedals are aimed to commuters/newbies and require less force to clip/unclip. I have the PD-T400 (my first clipless pedals) and though they unclip easily (for example if I'm about to fall I just pull my feet off the pedals and it unclips) but not so much that it unclips accidentally mid-ride when not intended. They have a platform so they're easy to get used to (the PD-T421 comes with a flat platform side if you don't always use cycling shoes).

The difference between MTB and road pedals is the cleat system. MTB used SPD which is a two bolt system and road pedals use SPD-SL (3 bolt). The shoes are also very different, MTB SPD shoes have recessed cleats so they're easy to walk in off the bike, in SPD-SL the cleat stand out from the sole so they're not as comfortable to walk in.