Highest osmotic pressure
You are correct in thinking that urea and sucrose would have van't hoff factor (i) = 1, since they are non-electrolytes and don't undergo disassociation(or ion pairing).

What you are left with are the following: $\ce{NaCl}$ , $\ce{BaCl_2}$ and $\ce{[Cr(NH_3)_4Cl_2]Cl}$. 

Let us begin with the the two chloride salts: $\ce{NaCl}$ , $\ce{BaCl_2}$. we assume 100% disassociation for the two (strong electrolytes) and we have i = 2 and i = 3 respectively for both.

Now, the complex would indeed disassociate but not completely (the extent would be determined $K_f$ for the complex). Thus 1 &lt; i &lt; 2.

Based on this, I believe you can order them on the basis of increasing osmotic pressure.