Those are definitely Mallards. If they were Rouens they'd be much closer in size to the Pekin, even if they are hatchery stock. Technically to have "Flying Mallards" you need to have the appropriate paperwork/license to have them as they are considered migratory. Clipping wings can be done but it would honestly be less of a headache in the long run to build a covered aviary/pen for the ducks with a wire or net roof to keep them contained. Ducklings can be pinioned to keep them from being able to fly, permanently, although you can't do that with adult birds.
Chances are the girls will get into mischief flying around. Hawks and other birds of prey could take them, they could wander off with some wild Mallards, and they could even be shot by someone hunting. Also, if you have any male ducks in the larger domestic varieties (Pekin for example) be sure the hens aren't being overbred, harassed, etc. From the photo it looks like you have all hens, but better be safe than sorry.
