Having trouble with 2 different classes

[Necrin]

So i'm an assassin, i think the most tough battles for me are destroyers and blade dancers.

And the only reason i'm struggling so hard is because of the invulnerability frames they have when they use their spin attack.

 

I can't seem to do damage or hit them with a stun, How do i engage them without falling into their AOE flurry and get knocked out of stealth?