Anyone who grades Duchess as bad is a scrub, plain and simple. She is one of the absolute best champs in the game.

Leave Kael at 50. You can pretty much ignore him, you don't need him.

Priority 1: Get Bellower to 60. He'll be your campaign farmer

Priority 2: Get Duchess to 60. She'll be your main dungeon support

Priority 3: Get Geomancer to 60. He'll be your boss killer

After that we'll see. Don't waste time leveling random people just for the hell of it. Level food and boost those above three to 60. Get masteries on all three. Fully book all of them. 

Thx again mate  ! Your advices are greatly appreciated !

Whoo that is a good thing that I ask because I would have went for Kael + Delianna + Geomancer + Warmaiden.

I am so sorry I don't have Duchess liltu on this account. I have marquess (def champ) that I see as yet another dommage dealer (I mixed up the tittles there and I will modify the original post) that is why some people find her good some bad (as Duchess lilitu is trully godlike). That change probably your all post as I am lacking a support (except bellower but he will probably be build differently to be the clearer).

For stuffing : I go lifedrain on geomancer (+acc) + Bellower (+speed) ?  

I am very surprise to abandon Kael that fast as I rerolled because I thought he would be a good option mid game and decent end game champ. In my main account I see a ton of Kael 60 in arena (with warmaiden). So I assumed it was the direction I was supposed to go.

Kael isn't bad. He's just easily replaceable. As a campaign farmer, Bellower does the job better, and as a poisoner, there's a ton of better options.

Marquess is just w/e. Ignore her.

Bellower -> Deliana -> Geomancer would be my new recommendation.

Nice thanks ! Obviously I wouldn't trash Duchess lilitu but Marquess I got a chance to see what she was. Nothing special. 

If you don't mind : speed + lifesteal sets for both bellower and deliana right ?

Bellower, yes. Deliana doesn't want lifesteal, she doesn't really hit that hard. I'd just focus on getting her stats up. You want her to have 200+ spd, 200ish ACC, and pretty high HP and DEF.

Sorry I meant Geomancer (what is wrong with me today xD Can't say one name right) : the lifesteal prock of the passive + hp burn right ? I may need an acc set on him for now to hit the HP Burn all the time

For delianna I like retaliation (given with log in reward) and Immortal (or maybe speed, immortal, resilience)

I can't be certain, but I do not believe that Geomancer's passive triggers lifesteal.

Immortal is good for Deliana, yeah.

This is correct, re: Geomancer. That was the nerf that hit him hard specifically in Clan Boss.