Try using an aperture of f/8 or smaller and a shutter speed fast enough to expose for the background. Also, HCE and equivalent photography stores sell softboxes that work very well on speedlights for softening light while you try and use the flashes as main fill. I would position the ladies so their facing away from the sun and trying an ND filter or polarizing filter may help as well. It's hard to say sometimes when not at the location, but go in with a smile and enjoy yourself. Make sure you shoot in raw to help with corrections. I would add, that if you have difficulties with over exposure, make sure it isn't too much or there will be some issues with recovering some areas of the picture.
Hopefully this helps a bit and good luck.
If you like, check out our site at
www.perfectsilhouettephotography.com and look through some of our daytime images. With bridals and sports we often get stuck shooting in open sunlight.