No, you can't increase a cooldown beyond the "base" Cooldown of the skill.  You could offset Fabian and Alice though so you're constantly increasing Cooldowns of the enemy.

Ok can they be used together? Let's say the max cooldown is 6 could Fabian increase the cool down by 3 and then another 2 by Alice making it 5 out of the 6? Or will the higher one simply take priority and it will only be 3 cooldown increase without adding the other one. Essentially can it be used together or will it only take the highest value even if the max cooldown for the skill is 6.

For ex like how if you do a 30% decrease def and then a 60% it doesn't stack or make it 90% it just keeps the highest value only.

Or is it like shield buffs where it can add onto each other but in this case, until it reaches the max amount (if it does).

Sorry for the paragraph lol just some 

yes, they can be used together. using both of their abilities will increase the cooldown of the opponents skills by 5 turns (or to the maximum amount if that's less than 5).

regarding shield buffs however, they do not add value to each other. there are champions with the ability to increase the value of a shield, such as brogni or emic, but just adding a new shield buff won't do that. it will keep the highest value one, same as with any other buff.

Yes, they would stack, up to the maximum amount for a given skill.

So lets say the target has an a2 with a 3 turn cd, and an a3 with a 6 turn cd.

Alice does her attack, and adds 2 turns to the cooldown of each.

Then Fabian goes to add 3;

The targets a2 would be at it's max, 3 turns, and the a3 would be at 5 turns