Praise be to Allah.
You have to try to keep the women separate from the men, even if the prayer-room is small. All the people – men and women – should know that the back of the room is only for women. You could put up some kind of barrier to define the space that is for women, even if it is only a line of the floor, or a marker, or something like that, so that there will be enough room for the men who come late to stand behind their brothers who came earlier, and in front of the women who are praying. And Allaah knows best.