The problem with having more than one hunting you is that, in theory, one or more boats can keep tracking you while someone else makes the attack run. Quick maneuvering and bursts of speed while the charges are actually going off should be okay - and you might want to try and work a depth change in there as well - since I don't think anybody's sonar is going to work with all the commotion in the water, but other than that I think you just have to run as silent as possible and hope they all lose contact for long enough to give up and go away.
Try using the rudder to make slow, looping course changes to port and then starboard while creeping away.
I had 2 of them after me once in about 70-80 meters of water and managed to get away, but I'm still not sure how I did it. They weren't very persistent, that's for sure. Good luck!
