I have NO idea how I'm going to do those rescue missions. Those are a paaaaaaaaaain.
Set game to Easiest difficulty. Problem solved.
Then you can ignore them on a second playthrough.
Can Trophies/Achievements be unlocked on Easy?
Most of them yes, with some exceptions (Finish Game on Hard with highest rank).
Oh that is hell. One of the rescue missions were damn near impossible because you fought that boss before doing the rescue mission. Somehow they expected you to get an A rank (or whatever it was) even though many of the buildings were already destroyed due to the boss battle. I gave up on that trophy altogether.
You just had to lure the boss as far away from the buildings as possible, closer to the sewer area. Then just rotate around it and shoot while avoiding the flame throwers. Might take a few attempts. ^^b