Here is what I'd do to compute the acceleration for C: write an equation for the dependency between B and C, or, rather between 4 variables [imath]x_B,y_B,x_C, y_C[/imath]. When you differentiate this dependency once you'll get an equation for the speeds of B and C; differentiating it again you'll get one for the accelerations of those two points. Speed and acceleration for B are computable relatively easily, then use your equations to get the same for C.
Something similar should work for the remaining questions of this problem.