did you ever have them rotated? if you dont rotate them they wear unevenly and it will cause this problem. you should rotate them at least every 10000 miles.
Also some brands of tires dont ast very long. If you get bad tires, dont expect more than 30 to 40 thousand miles out of them
inside camber needs to be aligned,just do a 4 wheel alignment,if you did this than i would look at the tie rod ends.or ball joints.the shakig is probably becauce the tires are worn unevenly.