I just used the Ladder Predictor found on the AFL website to work out what results need to occur to see which of the 5 teams remaining fill the 3 spots up for grabs. At the moment, the Ladder looks like this:
6th: St Kilda - T42, 108.3%, P20
7th: Sydney - T42, 106.1%, P20
8th: Essendon - T42, 99.6%, P21
----
9th: Nth Melb - T36, 104%, P20
10th: Fremantle - T36, 87.5%, P20
Here is what I found (margins are by the Predictor's default, which is 12 points).
Simple Scenario
Collingwood defeats Fremantle
St Kilda defeats North Melbourne
Essendon, St Kilda and Sydney automatically qualify for the Finals regardless of the results of their remaining games.
Likely Scenario (aka "St Kilda Scenario")
Next Week
Collingwood defeats Fremantle
Geelong defeats Sydney
North Melbourne defeats St Kilda
Essendon defeats Port Adelaide
6th: Essendon - T46, 100.2%, P22
7th: St Kilda - T42, 107.1%, P21
8th: Sydney - T42, 105%, P21
----
9th: Nth Melb - T40, 104.5%, P21
Fremantle cannot make the Finals.
Following Week
Sydney defeats Brisbane
Carlton defeats St Kilda
North Melbourne defeats Richmond
Essendon has the Bye
6th: Sydney - T46, 105.4%, P22
7th: Essendon - T46, 100.2%, P22
8th: Nth Melb - T44, 104.9%, P22
----
9th: St Kilda - T42, 106%, P22
In this Scenario, Sydney would face Essendon at the SCG, whereas North Melbourne would likely face Carlton at the MCG(?) providing West Coast win just 1 of their final 2 matches. They face Brisbane (A) and Adelaide (H), so it's highly likely.
Essendon Scenario
Next Week
Collingwood defeats Fremantle
Geelong defeats Sydney
North Melbourne defeats St Kilda
Port Adelaide defeats Essendon
6th: St Kilda - T42, 107.1%, P21
7th: Sydney - T42, 105%, P21
8th: Essendon - T42, 99.1%, P22
----
9th: Nth Melb - T40, 104.5%, P21
Fremantle cannot make the Finals.
Following Week
If North Melbourne defeats Richmond, Essendon are out of the Finals. The only way they may survive is if Sydney/St Kilda get absolutely crushed by Brisbane/Carlton, which is HIGHLY unlikely.
Sydney Scenario
Next Week
Collingwood defeats Fremantle
Geelong defeats Sydney
North Melbourne defeats St Kilda
Essendon defeats Port Adelaide
6th: Essendon - T46, 100.2%, P22
7th: St Kilda - T42, 107.1%, P21
8th: Sydney - T42, 105%, P21
----
9th: Nth Melb - T40, 104.5%, P21
Fremantle cannot make the Finals.
Following Week
Brisbane defeats Sydney
Carlton defeats St Kilda
North Melbourne defeats Richmond
Essendon has the Bye
6th: Essendon - T46, 100.2%, P22
7th: Nth Melb - T44, 104.9%, P22
8th: St Kilda - T42, 106%, P22
----
9th: Sydney - T42, 104%, P22
In this Scenario, Essendon would face North Melbourne at the MCG(?), whereas St Kilda would likely face Carlton at the MCG(?) providing West Coast win just 1 of their final 2 matches. They face Brisbane (A) and Adelaide (H), so it's highly likely.
Fremantle Scenario
Next Week
Fremantle defeats Collingwood
Geelong defeats Sydney
North Melbourne defeats St Kilda
Essendon defeats Port Adelaide
6th: Essendon - T46, 100.2%, P22
7th: St Kilda - T42, 107.1%, P21
8th: Sydney - T42, 105%, P21
----
9th: Nth Melb - T40, 104.5%, P21
10th: Fremantle - T40, 88.7%, P21
Following Week
If Fremantle defeat the Western Bulldogs, they can only make the Finals if St Kilda, Sydney and North Melbourne all lose OR only 1 of them wins. If 2 of them win, Fremantle cannot make the Finals.
Surprise Scenario
Next Week
Fremantle defeats Collingwood
Sydney defeats Geelong
St Kilda defeats North Melbourne
Port Adelaide defeats Essendon
6th: St Kilda - T46, 108.6%, P21
7th: Sydney - T46, 106.5%, P21
8th: Essendon - T42, 99.1%, P22
----
9th: Fremantle - T40, 88.7%, P21
Nth Melb cannot make the Finals.
Following Week
If Fremantle defeats Western Bulldogs, Essendon are out of the Finals.
OR
Next Week
Fremantle defeats Collingwood
Sydney defeats Geelong
North Melbourne defeats St Kilda
Port Adelaide defeats Essendon
6th: Sydney - T46, 106.5%, P21
7th: St Kilda - T42, 107.1%, P21
8th: Essendon - T42, 99.1%, P22
----
9th: Nth Melb - T40, 104.5%, P21
10th: Fremantle - T40, 88.7%, P21
Following Week
If Sydney lose and St Kilda win, they swap positions and end 6th & 7th no matter what. If they both lose, Sydney stays 6th.
If St Kilda lose and only North Melbourne/Fremantle win, they finish 8th and Essendon don't make the Finals.
If St Kilda lose and both North Melbourne and Fremantle win, both St Kilda and Essendon don't make the Finals.
If both North Melbourne and Fremantle lose, St Kilda and Essendon make the Finals regardless of St Kilda's result.
So yeah, there are the various scenarios. Many of them could be a little different, but the named Scenarios are if those teams lose their emaining games but the other teams results continue by the "Likely Scenario". Obviously the final Scenario is quite unlikely, but it's interesting to see how just 1 result can change so much.
Just so you know, North Melbourne don't have their own Scenario as I have had them win their remaining matches every time, so basically their Scenario is intertwined with the rest. That's just how it worked out wierdly enough.