Okay, I've shot a stack of these. You can use a plain white backdrop, but someone WILL be wearing a white dress or a white suit. The best backdrops I've seen are the coloured spotted ones, believe it or not. 3x6 metres will be too small. You'd be better to get another 3x6 metre backdrop and either get it stitched along the long side to slide along the back drop stands, or clamp it along the long side. Use one on the floor and the other on the stand with tape joing them at the floor. Get some extension sections from Photogenic. Use masking tape to stick down the floor section to
stop it bunching around the feet. Stretch the backdrop to remove creases. Someone here laughed when I suggested they dampen the cloth to remove creases, but that actually works.
The reason I suggest the bigger size is that often the whole family wants to be in the shot, and nothing is a bigger PITA than pasting backdrop behind then when they won't fit.
Don't set your light6s too far back from your subject, and make sure they stand away from the vertical section to soften the shadows. Something like F8 @ 1/60 to 1/125th will do the job. Shallower
aperture can cause an issue with more than one subject as someone will not be in
sharp focus.
Ideally, I'd use three lights, but two will do a reasonable job.