I'm not an expert but I believe you would have less hassles with 2 females. I also have an adult m/f that are a couple and act as a couple. Partners for life the way it looks. Very conscious of where and what the other is doing. 2 females are a little less rattled by brief separations. I can't go around the corner with the male, or the female has a tantrum.....or vice versa. As soon as one is out of sight....the other freaks out. The male will climb out or escape his enclosure to follow and see where his girl went. Real insecure...I've talked to him about that but he ain;t listening. She's actually worse. They're pretty much joined at the hip...keel?
The 2 young females are not nearly so worried over each other. Its kinda strange. They (M-F) are a lot like jelous people.
A kiddie pool works well to help contain ducklings when they are small yet give them some play room and them move it outdoors for a pool when they get larger. Mine learned to swim in the bathtub then got to know the pool and finally the pond when big enough. I used the old towels in the kiddie pool when it was an indoor duck pen and now use the same towels in the pipe pen. The pipe pens shape is always determined by the space available, and so that the towels fit well...like now, the pen is wide enough to have about 2" of towel on both sides. Then 3 laid end to end so the length of the pen is covered. Each afternoon, I simply roll up towels, lay down fresh "linens" and replace the food/water bin. Sometimes I'll throw a couple rags in there for them to cuddle up with. I have seen Bug wrapped up like she was in a blanket. Don;t let the lack of hands and fingers fool ya....that beak is very helpful and a duck is fairly resourceful.
As far as an inside temporary pen, the PVC frame that I made cost less than $20, is expandable, can be reduced, made square or rectangle, and can be disassembled for storage after a wipe down. I use the plastic garden fencing around it...that seems like was around $25 for about 20ft IIRC....it was'nt bad. The home made pen was lots cheaper than other things they sell for inhouse small animal containment. I think my 3 tier kiddie pool was $12...and I would inflate one ring until they could step out, then I'd inflate the 2nd ring until all 3 had to be used. The pool was good for about 6 weeks indoors until they out-grew it. Once they could fly over the 3rd tier which was about 12-15" high I knew it was hopeless and had to then build the pvc pipe pen which was as tall as I needed it to be and I could cover the top to discourage "adventures" when I was away. I was quite shocked the first time the drake flew up and out of the pen in the house and TO me where I was sitting across the room..! Impressed as well...I had no idea that he had been taking lessons. He'll do that when we're at the pond....if he gets too far away, he'll take the short cut and fly to me and try to land on my shoulder.
I bet I've changed the shape of that indoor pvc pen 20 times...whenever furniture gets rearranged the pen does too...to a shape that fits the space they will take over. I used 1/2" pvc and got a collection of elbows and T joints and DO NOT glue any of the pieces so it can be taken apart later.
They just got relocated to a nice long space behind the couch in front of windows with a great view of the pond...before that they were opposite a window where the 2 adult birds would sit and look at the 2 ducklings like it was a movie...Its a comedy show everyday, thats why I love 'em.
I'm retired.
Thats how I have the time for a couple duck babies inside. If I were still working...I dunno. But thats not an issue for me, so I can give the "kids" the entire day if thats what it takes. Once they get to adult size they become more independent. For now, They're all happy, I'm happy. I just wish they learn to fold towels........and maybe vacuum. Heck, could'nt get the ex to do that, dunno why I thinkin I'll get a duck to cooperate...