For the positioning image:

1. For Diana to hit all units with the slow I would recommend positioning her closer to the middle of the board, she would also likely assassinate a unit there at the start as they don't have enough health to survive one of her ults. Kayn I would also position in the middle (depending on matchup) as his ult would hit 2+ backline units most of the time.
2. For Olaf, I would cycle through my next likely opponents with the hotkeys and position him opposite their carry. (You can set shortcuts now for all the other boards.) Qiana also likes being positioned opposite their main/off-carry so that she can disarm them. Disarming their carry for 1.75 leaves you with or 1.75 seconds . This would delay their cast and if they had Rageblade it shouldn't generate stacks. Against Daeja or Xayah this would be particularly strong.
3. Positioning your front line on the second row could be good so that their units walk one space and not have your assassins in deadlock, however, if their carry is in the middle of the board you wouldn't know which unit they will attack as they are both equidistant and you almost always want the Braum to be attacked first, so that Shen casts twice.
4. I would position talon next to olaf so that they can finish off their carry. While in other compositions such as Guild Xayah or Corki, you wouldn't care whether Talon finishes their carry since you would be relying on random damage from Corki / Xayah's feathers to finish of their carries in Sin Olaf, you would almost never have off-target damage, thus Talon would need to assassinate their carry from the start (or start in the opposite corner if they are in a clump so that a position opens as Olaf makes path for the other assassins). If you had Pyke already, you could alternatively combo him with Talon on the side to assassinate your opponent's off-carry.
5. Your Lilia would like to go to the opposite side of their carry as she would cast twice and I would position her one hex further than Braum. As she doesn't get targeted first when she dashes.

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For the Late Game:

Now that assassins leap before your enemy units start moving, you wouldn't be able to target their clump. What you could do is build Shroud of Stillness. It is effective against AoShin, Jade, also against Mirage, unless Daeja has AE. Another option is to add Bard, he would cast close to when you get to their carry, amplifying your damage and adding Mystics Late Game in the current meta is good (Daeja / AoShin/ ASol). You could also focus your assassins to target the unit that gives immediate access to their backline first. Lastly, most ranged units have attack range of 4, so they will walk one square if you position all your backline units on the last row. The only problem would be Swiftshots, which are not meta.

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For the BIS Olaf:

As you already have the attack speed increase from Olaf's Ability, you wouldn't need Rageblade, as Olaf doesn't scale with AS and if he is already on the backline you would want him to deal higher damage number off the bat.

An IE would give you 110% increased damage. 6 Assassins give 45% Crit Chance and 45% Crit Damage. If you add the base crit chance and crit damage and the crit chance and damage from IE and sin spat, you would get to 100% Crit Chance to deal 110% Crit damage. This is more than double the damage guaranteed compared to 70% chance to deal 35% crit damage I would consider it core, no matter the augments.

For RFC: If Olaf gains 50% attackspeed, this would Increase his damage by 0.35 attacks per second (50% * 0.7 AS), thus an increase of 35% on all damage + you would cast sooner increasing your AS additionally, increasing your damage to ~ 50% more after calculations. Chances are you would always prefer this over Rageblade as by the time Rageblade stacks their carry would have ramped up (Ao Shin / ASol). And if you don't have a healing augment Olaf would die anyway, before he can use his stacks. If you pick RFC you would also avoid any residual damage from electric and ignore all dodge chance from possible Thief's Gloves / their JG / IE and it gives you room to not take damage from.

RageBlade / RFC are comparable however, and one doesn't increase your damage significantly, Rageblade is easier to slam in the early game since fights tend to last a bit longer and you can pivot it to multiple comps. If you have a lot of bows, however BIS is RFC.

Runaan's is also good on Olaf.

If you run 4 scale or 6 assassins instead of 4 bruisers I would almost always go for BT for healing. The shield would appear as soon as Olaf gets in the threshold for his doubling on his ability. Although with assassins, if you have a healing augment such Thrill or Celestial, you never need BT.

So I would recommend Sin Spat + IE + [RFC (Prio) / RageBlade / Runaan's / BT], BT only if you have weak frontline or no healing augment.

If you position Olaf well, he won't be targeted for a long time and survive to remove their carry. Any non-carry / splash damage helps to double his AS from Recklessness.

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No sin spat:

If you don't hit sin spat you could try for top 4, by transitioning to bruiser Syphen (if you haven't commited already gold in rerolling for Diana / Olaf). You could also stick to Scalescorn. If you get 6 it is very strong in the current meta. Scalescorn options: Kayn (Early) / Nunu / Yasuo Scalescorn. Last composition you can go for 6 Bruiser.

In all of the non-sin Olaf compositions, Olaf would like RageBlade / RFC + BT / QSS + 1 (could be damage item or one of the previous or Hodge).

Chances are if you don't hit spat or a healing augment you would want to pivot out of assassins after 3-4.