family history can influence the chances of having twins to some extent but just because of that we cannot predict that whether you will definitely have twins or not,
as you are under treatment for poly cystic disease,
if you want to conceive stop taking contraceptive
pills and go for ovulation induction
drugs with your doctor's advice.
if you take the ovulation induction drugs in the early part of cycle means from 2nd day of periods to 7th day, there is chance for maturation of more follicles which can increase the possibility of twins.