I'm not sure as it was a while ago I did this bit but I think the barriers are arranged in such a way that one is isolated from the other 3. If you look you'll see one doesn't really move much and you can move through gap in the barrier division to get to it. Kill that one separately then use the B attack to kill the other 3 together, making sure they're not near the barrier or you could interrupt the attack by accidentally hitting it.
Hope this helped.
If you're referring to the bit where one of the beasts is seemingly behind a barrier then
theres a gap where you can get to him along the left of the barrier, go in kill him leaving the other two then use the Z attack to kill the other two. Thats a general tactic for all the others, even when you get up to 5 beasts just single attack til you're left with 2 and then Z attack
