Agree with the above. You can do a LOT with a single Speedlight, and even more with two or three. Practice, practice. Three weeks is not a ton of time but if you can figure out exactly one setup that works, you can apply it to individuals on the whole team. [IMAGE'S LINK: https://flic.kr/p/pUw9Xz]BBB_Cabaret_20141031_30909.jpg
If budget is a constraint, skip the well-constructed but expensive Canon branded stuff and go for Flashpoint gear. For the price of one 430EXII and some way to trigger it off-camera, you can get three Flashpoints, or two Flashpoints and enough grip gear to get going with a portable portrait setup.
MalVeauX linked you to a lot of good stuff above. I personally prefer softbox-style umbrellas with a permanent front diffuser, instead of the convertible ones, but the convertible may work fine too. Here are the ones that I use:
I also like my standard umbrella adapters, but that Godox holder linked above is really interesting - I haven't ever seen it before.
For your immediate need, your big objectives are:
1. Figure out how to position your light(s) so that they're flattering on most subjects;
2. Figure out how to position the subjects, lights, and yourself to make any space work as a studio.
1. my go-to fool-proof setup is to position the softbox so that the bottom edge of the softbox is about nose level, and it's just far enough left or right so that it's not quite intruding into the framing of the image. if you have a second light, use it as a rim/hair light or a background light. If you have a third light, now you have a rim/hair light AND a background light - OR you can use #2 and #3 as left/right rim lights - this is great for edgy photos of athletes.
IMO, the easiest and most common thing to screw up is to put the main light too low. You want to light the subject slightly from above, so the shadows fall under the nose and chin - this is what we naturally expect to see, because the sun is overhead and indoor lights are overhead. If the main light is too low, it won't be flattering - it's hard to sculpt the jawline, eye bags will be severely pronounced, and shadows going up the face instead of down the face is simply weird.
2. If you use your longest lens, perspective becomes your friend, and you can use a small section of blank or plain-textured wall as a studio-style backdrop. If you use a wide lens, perspective works against you: you see everything in the background - and studio-look shots become practically impossible.
Go scope out the team meeting space and figure out where you can shoot. You need a long skinny "alley" to shoot down, with a blank wall at the end. Everything else doesn't matter.
Here's a sample behind-the-scenes shot of a performance venue where I take a lot of performer portraits. For a backdrop, I use the slab of black-painted plywood that's covering the air handler, it's a standard 4x8' sheet (tiny, as far as backdrops go). This is a three-light setup (main light in brolly box; kicker light in shoot-thru umbrella, backgruond light sitting on the floor, gelled but no modifier), but if you find a white or neutral-colored wall, you don't even need light #2 and #3. Click to the next photo in that album for a second perspective of that setup.
I'm shooting from as far away as I can manage - the performer stands where my color-checker is sitting on the floor (a bit in front of the background light), and I'm way on the opposite side of the stand, shooting at 135-200mm. This makes the black plywood look very large relative to the performer. If I stand close and shoot at 35mm to get the same framing of the subject, you're seeing alllll that other clutter behind the subject - unacceptable.
by Nathan Carter
, on Flickr
And here's the results (this is with a blue gel on the background, instead of orange gel as shown above): [IMAGE'S LINK: https://flic.kr/p/GN7DgX]Cupcate_Burlesque_20151120_5894.jpg
by Nathan Carter
, on Flickr
I was shooting video for a little music video, and the still photographer didn't show. So I had to cobble together a workable portrait session using just what I had in the trunk of the car, and what I could scavenge from the costume designer's house. We shot it in the costumer's SUPER CLUTTERED living/dining room, but I moved some chairs out of the way to find a little bit of wall space that was big enough for individual portraits - again, no bigger than 4x8', and painted seafoam blue-green. Fortunately, the ten-foot white ceiling worked to my advantage here.
I had one speedlight, one stand, and some assorted clamps and stuff in the trunk of the car. I found a plastic tupperware lid in the house. And I made it work. The light falling on the subject is a combination of bouncing off the plastic lid (main light) and bouncing off the ceiling (fill light).
I stood on the far opposite side of the room, again using a long lens. The dining table was between me and the subject, so I just shot over it. Impossible to get full-length shots this way, but headshots and 3/4 shots were absolutely achievable.
This should be publicly viewable - scroll down in the comments for a little better behind-the-scenes shot.https://www.facebook.com ...45/posts/1262281613840947