I need Help duck breeding?

I have bought a pair of blue swedish and a pair of mallard ducklings and now they are 6 to 7 weeks old and my blue swedish pair are already standing beside each other and coupling up and all of the ducks come up to me when i feed them in their cage and let me pet them except for the mallard hen . so she just hunkers up behind the other ducks like their her mom and she is the smallest one out of all of them so i dont know what to do.I am also planning on breeding the blue swedish and and selling the chicks but i was going to breed the mallards once or twice and let them out on my pond to live there. plus if i mated the blue swedish whith the mallards whould that look like a pretty duck or not?