CJ, if I were in you shoes I would call or visit the client and/or the web designer and discuss their requirements in great detail, down to the number of images required, and what's on each of them, what the images are going to be used for, whether you can rearrange furniture, etc, etc. You may be surprised by what the tell you, and how different it may be from what you thought. It would be best to understand what message or "brand" the law firm wants to project with the website and the images. You said they are in a hurry but if the images are not what they expect you'll be in a world of hurt - take your time to really understand what needs to be done.
This is a typical picture that projects strength and confidence - group of lawyers in an fancy conference room:
Texas Probate, Will Contests Lawyers TX, Estate Trust Litigation - home page
Here the designer used architectural elements on the banner to convey stability and "contemporary outlook"
Dallas Business Law Attorney | Fort Worth Debt Collection & Litigation Lawyer | Texas | TX - banner but note that the portraits of the lawyers under Attorney and Staff are awful.
The color palette the designer has chosen for the website should also be considered when doing your images. The better you understand all these elements, the more likely it is that the images complement and "fit" into the overall idea.
Concerning light, I'd say that strobes is the way to go, and two should allow you to do the headshots and the office portraits, as long as it's not a large group. Umbrellas are your friends! Dont mix lights, use only strobes, unless there are huge windows and you want to use that light. It's pretty hard to deal with multiple colors at the same time unless you have plenty of time to gel flashes or tungsten light bulbs...
Good luck!