Your ducks look lovely and its great that they eat out of your hand. The new bigger pen that you are constructing will be great for them during the day -- with a kiddie pool in it as someone above has recommended. I also suspect that they are nervous about coming outside as it is very open. They will need a warm, secure duckhouse in the winter -- whether you get htat now or just bring in some hidy places is up to you and your purse. I am in a warmer climate [NE Florida] and so my duck coup is made with metal ribs and small chicken wire. I have a translucent tarp over it from the ground on one side to the ground on the other, but the tarp is turned up on one side in warmer months. I still need to provide for extra warmth in the winter and have a wall cabinet without doors that two or three can sleep in. I also bring in bales of pine straw in the winter. You could put an old cabinet in the new bigger run for your ducks, that they could hide inside. or put a tarp over the roof.
Like you, I spend a lot of time with my ducks. They don't like being picked up -- although I can pick them all up if I need to. They like me to sit down on the middle step of three steps at the back of my house where they can stand above the step I am sitting on. But they will come and stand by me and let me pet them and, they will come up in front and eat from my hand. One of my drakes strongly dislikes being touched -- he is really nosy and wants to look in the house and see what I am doing, and come and stand near me when I am sitting on the steps. But he just does not want to be touched. That is the way some ducks are. Also, my drakes are all more comfortable being petted than my son's females are. His females will all eat peas and mealworms from my hand but only one -- a muscovy -- likes to be petted. And the muscovy is currently broody and won't let anyone touch her!!! I think that is common that drakes are more relxed about being handled and petted than females.
So my advice is -- get a stool and sit down with your ducks; and don't expect to be able to cuddle them. Be happy that they like your company and will come round and eat from your hand. I bet they will start nibbling your toes/shoes if you sit down with them regularly.