I love your use of the brush pen to give a really bold and economical mark. Having the confidence to go straight in with the pen gives your figures a bold, eye-catching style. The choice of colour on the off-white background is also very appealing. It gives you drawing a softer, warmer and more natural look than black on white.
A benefit of brush pen is that you can add in some really hard areas of contrast and shadow. I think that something like that would look great on your drawings. When you have finished with the contour, you might consider adding in the very darkest areas as blocks of colour, to really play to the brush pen's strengths.
Speaking of strengths, you do a great job with varying line weight in these figures. In the bottom left, your thinner, lighter lines around the figure's legs draw the viewer's focus in the direction she is leaning and pulls the centre of gravity forwards.