Outdoor group portrait setting
if it's late morning, the sun will be up in the sky, directly above everyone. It's bad because this will cause harsh shadows under the eyes and nose (Racoon eyes!). Try to take the picture in the shade, or wait for clouds to cover the sun to soften the light to prevent the harsh shadows.
In terms of lens and settings, I don't think you'll need the wide aperture of the 35mm anyways, since it's going to be bright and you would want everyone in the group to be sharp. So i would go with the 18-200mm. I would also set the the aperture to at least F/8 or F/11 so everyone in the photo comes out sharp. If you do use the 35mm, stick with smaller apertures like F/8 or F/11.
As for the focal length, I would suggest you use somewhere in the midrange, let say around 40-50mm, and go back as much as you can to fit everyone in the frame. I wouldn't use either extremities of the focal range as 18mm might introduce barrel distortion while the 200mm is probably too tight of a frame and probably has pincushion distortion as well.