I my magic dosage was 8 pills per day, or 80mg. It really depends on the person. I am currently weaning off the pills because my supply seems plentiful & stable (OMG YAY!) and am down to 5 pills/day.
My nurse friend has said that 80mg/day does the job for many women and its a good place to start. I personally started lower and when I went up to 80mg, it was perfect. You have twins so I'm not sure how that factors in--80mg might be enough. You're just basically teaching your body to produce more milk.
Here's some info for you:
Some Aussie thing that I can't say is good or bad
Another website on dosage.
Keep us posted!