What is the DP composition of Vivinal® GOS? Is the oligo fraction of all products the same?

Yes, the oligosaccharides are the same in all products.

DP composition (on weight percentage of oligosaccharide)
DP2 (other than lactose) (%) 31
DP3 (%) 38
DP4 (%) 18
DP5 (%) 8
DP6 and higher (%) 5
Total (%) 100