Marion, I certainly identify, went into nearly the same situation about 2 years ago. Mixed group of men and women. Don't you know, I had to learn a whole lot about transposing in a hurry! It is a challenge to find a key. The men are happy with one, but the women find it hard; then when you try a change, it's vice -versa!
And I agree with the BOOM-chuck approach. The singers need a basic reliable same-every-time accompaniment.
Tell you what I did. I approached the very best singer in the group and asked her help so that the group would be a success. So we work together on a few songs ahead, to get them in the most singable key. Then during the jam, when something does not sound right, we stop and the two of us figure out something else to try.
The advantage is I can key on only one person telling me what to do, and it is someone whose skill I trust.
This is just my particular experience, it may not apply to your situation at all, but I put it out here in hopes it may. -- the canoer