I been asked to take a group photo and would like to take a good one but unsure about how I should go about it.
I have a 24-70 2.8 and a 50 1.4
No strobe but have a few flashes
Should I place the group in shade that is back lit and fire the flash from my camera to light up the eyes? How should I approach this?
Avoid shooting a group at low f-stops. Low f-stops create shallow depth of field, but when shooting a group, the subject will all be at slightly different distances. If the team is organized into a couple of rows of 4... then you can end up with a result where the front row seems to be in nice focus, but the back row is a bit soft.
Since there's probably not much reason to need to shoot at flow focal ratio (you're probably not attempting to create a deliberately blurred background and if you are then use a suitable neutral density filter), I'd probably pick f/8 of f/11 (f/11 if using flash).
Depending on "which" 50mm vs. "which" 24-70mm lens you have ... the prime lens might not be any sharper than the zoom. You may find the zoom is more versatile. I generally prefer the "look" of shooting from farther away and being a bit more zoomed in (e.g. the 24-70 but zoom to the 70mm end and back up to frame the group -- but that's me).
If subjects are looking into the sun, they tend to squint. But if the sun is off to the side or behind them that can produce either dark shadows or some under-exposure and if you bring up the exposure, the background may be a bit too bright.
Shoot in RAW to maximize your ability to adjust shadows and highlights.
You can use a flash (assuming it's powerful enough) to fill in shadows so the subjects don't seem too dark. An "on camera" flash (pop-up flash) is usually only adequate to light subjects at close range. A shoe-mounted flash with a more powerful strobe will often have enough power to do the job.
But if you're using a flash in mid-day sun, keep in mind that the sunny-16 exposure says that at f/16 the shutter speed is the inverse of the ISO. So assuming ISO 100 and f/16, that's 1/100th sec. If you open up to f/11 then the shutter speed (at ISO 100) increases to 1/200th. If you shoot at f/8 (per my example earlier) NOW suddenly you're shutter speed is 1/400th and that is likely faster than the camera's flash-sync speed (most cameras top-out at somewhere around 1/200th to 1/250th sec). If you turn on the flash's "high speed sync" feature then it cuts the flash's power (because the flash has to burst multiple times while the shutter slides across the sensor - meaning no single burst of light can be too strong because the flash has to reserve enough power for every burst it makes). SO... you may want to use f/11. BTW, some camera's max flash sync speed is only 1/160th and sometimes third party flashes and triggers aren't as quick to respond and force you down even slower. Be aware of that and check your images.
If the subjects are out of the sun then you don't have to use a sunny-16 exposure rule. However... one mistake I sometimes see is a photographer who gets the subjects "out of the sun" by putting the subject in the shade... but then there's still "background" in the image that is in full sunlight. What you end up with is a nicely exposed subject and a completely blown out background. So if you want to get the subjects out of the sun, for purposes of opening up the aperture, then you'll want to make sure the background is also out of the sun.
I have done outdoor portraits where I didn't want to use high-speed sync so I used an ND filter to block enough sunlight to allow me to use a wider aperture and still be able to light the subject with a flash at a slow enough shutter speed to avoid using high-speed sync. The key benefit of an ND filter is that it changes the range of exposures that are possible.
Good luck!