First thing that comes to mind is placing one flash unit to the right and another to the left, but the subjects in the middle of the row would get light equally from both flashes,in an unflattering manner? An if a third flash is placed aiming towards the center of the group, then the subjects near the middle would get light from all angles and more intensively?
They key is to use modifiers, such as a fairly large umbrellas, to soften the light so that it is more flattering than hard light from both sides would be. Place each of the two lights in front of each end of the line and aim the center of the light's coverage halfway from each end to the center. Also try to get the lights as high as is practical (up to about 10-12 feet if your subjects are standing adults) and placed far enough back that the person in the middle is about 1.4x as far from the lights as the persons on each end are. Make sure the coverage of the flashes are wide enough to cover from the end to the middle of the group.
Indeed, you need more than one light, otherwise the whole group will not be lighted evenly at all (unless hypothetically you have a very powerful one placed far with a big light box - you didn't specify strobe type, studio, cobra ?), and you risk red eyes, glasses reflections, etc...
As indicated light shaping tools like a softbox would help getting a more even light on your group. The bigger, the better.
Assuming 10 people slightly crowded together, let's say in ~3m width, and supposing you are using a 50mm lens, so that you are about 3 or 4m away from the group. First possibility, your idea : two lights, at your level, symmetrically ~0.5m to each of your sides, facing the people but if possible placed at at least 2m high or more (in order to avoid red eyes and ugly shadows and highlights ...).
Second possibility, again two lights : put them symmetrically separated by ~3m, 2m away from the group, both pointed roughly to the center of the group (~30° angle) in order to get an even amount of light - this is a mix of calculation and intuition, since light intensity decreases proportionnally to the square of distance. The height is important again.
This assumes that the lights yield roughly the same intensity on their whole field (probably not the case with light shaping tools). Otherwise it gets trickier, and experimentation is the key.
Just an alternate idea : could you not place them on two rows (taller behind, in the spaces between the first row people) ?