@lovemy mallards You put a few questions in ovations, so I will try to answer them here:
Ducks can hold their breaths about as long as a person can from what I have read, but they can get a breath very fast when they surface. Since the female can rock the boat so to speak, I doubt on open water one duck can drown another even with a large size difference. But in shallow water a heavy duck can maybe hold down a much smaller duck and multiple ducks ganging up on 1 duck can definitely cause problems.
I am more concerned with my kiddie pools than the big one because the duck on the bottom can be pressed on the bottom of the pool - in deeper water, she can always rock back and catch a breath unless multiple ducks hold her in place.
For the most part, we don't. We either just break them in half or cut them into spears, then hold on to them so the ducks nibble off bite sized pieces themselves. They have duck food available all the time, but we "bring" them the treats and hand feed just about everything but watermelon. That way they always love seeing us

Snow is no problem at all. They have a straw patch available to them near their house where they can stay if they want to be outside but out of the snow and when it is REALLY cold, they pretty much stay on it, but otherwise they just go where they like.
I am ashamed to say it, they get meal worms almost every day. It is probably a bit much, but they love them so much! We have 12 ducks and go through about 88 lbs of dried meal worms per year (I buy them 44 lbs at a time). They get more in the winter when it is their primary treat after romaine lettuce. In the Spring/Summer/Fall, they get more watermelon, butter lettuce, cucumbers, tomatoes, gold fish and of course they still get romaine and fewer meal worms (but still almost every day).