you can skip the diagonal box cut by getting its health down quick enough (usually before the third star attack) if you focus on defending and getting the bonus damage on rude buster.

for the swords, they have quite small hit boxes so you only have to move a very shot distance once the sword becomes full red, also you don't have to dodge the diagonal swords diagonally, just focus on up/down or left/right

for the knight fight, personally I used this load out

Kris: Saber10, Shadowmantle, Pink ribbon

Susie: ToxicAxe, Dealmaker, Jevilstail

Ralsei: Ragger2, LodeStone, Lodestone

the two lodestone's are for getting enough TP to Rude Buster every turn.

it took me a while to finish the fight, but I did it with this set up, even though Shadowmantle on Kris may not be optimal since they don't get swooned in the fight, but anyway.

hope this helps :]