I did try that (HSS), and it works if you have 4 or less persons (looked great for 2 persons, but was stretching it for 4), but some of the group shots had about 10 persons (I should have mentioned that, cus I didn't have an issue with the photos of the couple only), so what happened was the persons on the edges (whichever points are furthest from the flash) were probably 1-2 stops darker than those closest to the flash (might be fixable in PP, but that is a big risk to take
I could have tried some kind of feathering, but even then I think you need more than one flash. Shooting off axis may have helped, but then I would just bias the exposure to one side or the other I think.
Maybe multiple small flashes, off camera would have done the trick (minimum of 2 small strobes maybe)? Really think that might have been the solution. I could therefore control the flashes independently, and created a lighting ratio that caused the most even light across the frame.
Been looking through the pictures, and this time it worked out fine, but maybe I was lucky! I probably need to find a solution quickly since next time might not go so well.