You can make sure that counterattack is always on by speed tuning your champs to the boss' speed (171+ for NM, 191+ for UNM- lots of guides online about this). 

I'd also recommend using Draco, Skullcrusher, Vizier, Coffin Smasher, and Lugan. Vizier can keep Draco and Coffinsmasher's debuffs up by himself and Lugan is there to keep your team alive. Tune their turns accordingly- maybe go Draco>Coffin Smasher> Vizier> Lugan> Skullcrusher. Good luck!

One Skullcrusher is enough to have CA up on both AoE turns. Your Draco is 153 speed, so the team is not speed tuned. 

Put all your speeds either in range 191-199 (better for UNM) or 171-179 (will have to manual 2 turns and miss CA damage on them, but will work for NM) with SC going last. 

Wouldn't speeding up my team make them loose faster? I probably have the whole wrong idea on this, but keeping them slower makes sure they don't outrun him, or my logic off? That sucks I'm not gonna be able 2 keep my draco that build then, he does 100k damage a hit +70k from his weakens, plus a counter so possibly 340k a turn, if I can take away sandslash and keep the counter I can't understand why I can't keep it on now, I thought her buff extend would make them work great 2gether, counter should never end I thought, but hasn't been working this way

Having them faster means they'll take more turns for every turn of the CB, hence they should do more damage. But the idea with counterattack (or unkillable) teams is that you don't make all champs as fast as possible, but you give them such a speed that they all remain in sync - that they keep having counterattack buffs on at the time of the CB's two AOEs, for every turn the CB takes. If you don't speed tune, they will go out of sync, still counterattacking sometimes, but sometimes also missing out on counterattack opportunities because they have it up while the CB is doing his single-target stun on another champ, then they don't have it anymore when he hits the next AOE. Moreover, it will make it harder to arrange for each stun to hit Skullcrusher at the time when he's got his unkillable up, which may mean champions dying earlier than they should. 

So of that lineup who should have what speed? Also does anyone know how speed boost affects? If I was to put a speed booster instead frost banshee would I be able to keep lower set speed meet the speed with a non-stop boost?

Skullcrusher the slowest, with the others it doesn't matter that much but ideally your weaken/decrease def champs first, like in the order Lxzy mentioned. 

Speed boost will throw the speed tuning out of whack because different champions have different base speeds and would hence get slightly smaller or bigger boosts. It's not recommended to use speed/TM boosters on a counterattack or unkillable team - in fact, even masteries that give you turn meter boosts may be an issue. 

Here is an old video of mine that will help hopefully.

https://youtu.be/ekh8yCoHRn4

II pulled sepchular sentinel a I was wondering if I speed tuned her for a 4:3 ratio, what speed would she need 1? And 2. Would sandslash be able to make her inc def last 3 turns while never loosing counter on sep