you can get separatly the minimal representation of each transfer function in the matrix, then you will be able to deduct A,B,C and D of the entire system. let Ai,Bi,Ci and Di, i=1,...,n be the state matrices associated to the transfert function i in the TFM, thus, the matrix A of the entire system is A = [A1,0,..0; 0, A2,0,..0;.....;0,0,...,Ai]; that means Ai are mounted in the diagonal of A. for B and C you have to respect which input and repectively the output are concerned by the transfer function i. the same for the matrix D.