Do NOT pose them looking into the sun unless you want them to have squinty eyes. Look at the light you have available and see what faults it has, then use your flash to "fix" those faults. It the sun is bright and causing harsh shadows, then use your flash as a fill light to fill in the shadows. If the sun is NOT bright enough, then use your flash as the main light and the sun as fill light. If the sun is inbetween these 2 extremes, then balance the light sources to please YOUR eye. You have the skills and talent, now get the confidence and do the job.