Don't be afraid to turn your flash up either, as you may need all it's got to overpower the sun. It's good if you can overpower the sun, as the background will look darker and hence the people will pop out of the shot rather than blend into a bright background.
Thanks guys for sharing your experience.. This is a basic good concept to remember.
Do I need color gel for my flash, to balance color with sunlight.
I might need ND filter, to battle sunlight..?
If you shoot a group, you probably need to stop down to get sufficient DoF to have the whole group in focus, so I would not worry about needing ND's. If you use a speedlight, you can use high speed sync allowing you to use shutter speeds above the x-sync speed of your body.
As mentioned by the others, it is best to have the sun somewhere behind the group. You can then overcome the shadows on their bodies and faces by using a flash (prefereblay with diffusor) or reflector(s), or a combination thereof. Reflector(s) will give you more smooth light like whith a softbox, but with large groups, you may need multiple relfectors to get an even illumination on the subjects. When using reflectors an extra hand to hold them in position is helpful. Some extra tripods to position them against may also work. Using "gold" reflectors may give you nice warm photos even mid day.
If you can place your group in the shadow of the tree, you will get an even shadow that is more easy to overcome than a mixture of hard lights and hard shadows on their faces.
I have no experience with on-flah gels, but can imagine that they offer the same potential as "gold" reflectors.
If you shoot in RAW, you can do quite a bit of color correction to balance colors in post.