MIMOI ss2tf, how to apply input to TF?

I have a system with 2 inputs and 2 outputs in the form of a state space model in simulink. i want to be able to represent cross coupling in the system by generating 4 transfer functions. However when using "ss2tf(A,B,C,D,iu)" i am only able to use "iu" values of 1 or 2. So how do i generate four tf's?

Next i want to apply a step input to TF11 (the transfer function representing relationship between input 1 and output1) and with nothing appplied to TF22 i want to be able to plot/observe the output at y1 and y2. How do i do this?

Do i need to get differential eqn of TF in order to apply an input to it?

I am very new to matlab so step by step help would be much appreciated (inc any codes that might be useful).

Thanks