Yeah, the Demonspawn 14 boss is unusually difficult - personally I have 3* on all DS nodes until 20, except on 14 where it remains impossible to finish without losing some champions along the way. There's no other FW where I've gotten that far without having 3* on the level 14 boss. 

Still, you have good champs and should be able to get 1* at least so you can move forward. Kymar and/or Umbral, Magnarr, Peydma are all good options, Alure is good in general though will die quickly on that boss, Nazana might help there too. But in general, you'll need high speed, one of the nasty things about that boss is how very fast he is. And then he has powerful CC and ignoring defense, so high defense won't do you any good but resistance and high HP will. If your Peydma is fast enough to go before him and ensure decrease attack remains up the whole time, that should help already. 

Thanks, still can't keep my team alive long enough. Best I've gotten is around 50%