Don't take any notice of one mounting the other - that is not a reliable indicator of sex. Females will do it to females. Definitely does not mean that the one doing the mounting is a drake.
A dark coloured blackish blue bill sounds like a female to me. Even the silver/splash females have a...
Your two ducks look like they are 'splash' or 'silver' Swedish, meaning they have two doses of the blue gene (black Swedish have none and Blue Swedish have 1).
There are no major differences in the appearance of male and female Swedish. In the blacks, the drakes have a greenish head. In the...