Here is my strategy / video guide to solve this mission. If you follow the strategy / video you will obtain "automatically" the Silent Assassin, Suit Only Challenge and eight other challenges (see list below)
My strategy is that I kill Dalia as first and then I kill Viktor and leave the mission. Ok here are the basic steps:
Dalia's Kill1) reach Dalia's bathroom in the third floor via pipe outside the building
2) Subdue the guard in the room next door via radio distract
3) wait that Dalia come back
4) distract Dalia's Bodyguard with a overflow sink
5) kill Dalia with Fiber Wire and hide the body
6) leave the area via bathroom and go in the basic / first floor
Viktor's Kill1) as we come down from Dalia, I go to the room with the Diorama and hide behind
2) wait that Viktor is close to the Diorama and insert a coin in the Diorama
3) when Viktor leave the Diorama, subdue the bodyguard near the door and hide the body
4) wait that Viktor cross the same door
5) kill Viktor with Fiber Wire and hide the body one floor below (basement)
6) leave the mission through the Catacombs exit (basement)
All Challenges in this vid:The Mastermind
The Moneyman
Piano Man
Silent Assassin
Silent Assassin, Suit Only
Suit Only
The Personal Touch
Suit Only
No Evidence
On to the Catacombs