First off, introductions: I've got previous mafia playing experience and I have heard that this is a high-skilled and interesting forum to play on and it should be nice to get to know you all. Now, to business...
The chances that there will be a scum pair is actually equally likely to the chances that there won't.
Let scum1 be placed on family1.
Now there is a 1 in 6 chance that scum2 will be placed on family1 and a 5/6 chance he will be placed in another family - let that family be family2.
Now there is a 1 in 3 (2 in 6) chance that scum3 will be placed on family1 or family2.
1/6 + 1/3 = 1/2.
Assuming the scum pair lands on family1, the families look like:
F1 = s1s2
F2 = s3t1
F3 = t2t3
F4 = t4t5
F5 = t6t7
F6 = t8t9
So the scum have between 5 and 8 votes depending upon how much townie1 trusts/agrees with scum3.
I haven't seen anywhere you posting about whether it is day or night start but I'll assume night as from my experience that is the norm.
N0: scum kill not-townie1 (townie2) - certain
D1: town mislynch not-townie1/3 (townie4) - 6/11 (raw odds only - haven't got the time right now for anything more complex looking at town strategies to deal with voting and the like, adjust depending on how highly you rat day1 scum hunting)
F1 = s1s2, F2 = s3t1, F3 = t3, F4 = t5, F5 = t6t7, F6 = t8t9
N1: scum kill not-townie1/3/5 (townie6) - certain
F1 = s1s2, F2 = s3t1, F3 = t3, F4 = t5, F5 = t7, F6 = t8t9
D2: town max voting power = 8, scum max/min voting power = 8/5, essentially townie1 swings whether the scum or the town hit their max voting power and so has to catch a scum right here or the town loses. Furthermore, if townie8 believes townie9 to be scum or vice versa and refuses to vote with them on the theory that they are townie1 in the above situation then the town's voting power comes down to 5 and the scum are at 5 themselves (6 if townie8/9 is voting for a townie) so here you get a random generator for the win if scum want it as best case scenario.
This leads me to the conclusion that optimum play is to vote as per usual and then to get everyone to pile onto the leading target at days end as there is a 3/11 (1/2 * 6/11) chance that this is what you get if you play with the voting system which I'm guessing isn't what you want as it removes the voting mechanic from the game.
This was written in a bit of a rush so feel free to quiz me about how I got any of the numbers/assumptions if you want.
Finally: whilst I am a bit of a maths nerd I insist that I am vaguely interesting to talk to and a nice (enough) guy
