There is one cardinal sin with negative exposures, underexposure.
So, a couple thoughts if you are going to shoot this type of lighting regularly.
You may need to consider higher EI's (pushing the 400) or a higher EI film like 800Z or similar.
Another really good option is a good flash like a Nikon SB-90 or similar that you can use to pop in a bit of fill light to light the people up better. Not a lot just some to get them off the toe of the film curve.
Thank you very much. I shall keep this in mind going forward. For violating a cardinal rule, my results werent horrific; just not what I expected.