Well, for starters , don't assign things to the same midi channel (if that is what you are saying).
Some questions: are you assigning a new instance of play per sound and track used, OR are you trying to use an instance of play with multiple midi tracks assigned?
Way # 1 works fine, and resolves the issues of midi overlap.
Way number 2 should be used like this: take your audio instaument with Play, and go to the environment, make a multi midi object, and attach it to the audio instrument. This way each midi channel in play should be assigned to it's own midi channel to start, and then you use the cabled multi midi to control where you send the data.
So midi channel 1 on the multi midi object (assigned in the arrange window to send data to play which doesn't actually have any data sent to it other than this way) goes to only the midi channel on play that it should.
Now, it sounds a bit confusing, but I have to say: read the manual, look at the movies at East West and Apple, maybe look at some of the paid tutorials at Groove 3 or Mac Pro Video. A person CAN NOT figure this stuff out without putting in the time, EVEN if you were to hire someone to come and do the actual setup work for you.
This level of Logic is much deeper than most, and like learning how to play and instrument, or read music, it takes a personal investment that simple cannot be answered in a forum post like this, sorry.