Thanks for the question. Please see the attached file for a possible solution. I've made the following changes.
- Removed the clipping splines and used the base spline to place the stairs instead. This is done by adding additional vertices and setting the stairs segment to a material ID of 2. You can then stop chairs from appearing here by turning in Limits in the generator's settings
- Wired the chair to the default input and added a padding of 50mm. As far as I can see you can either have a fixed spacing value OR a fixed number of chairs. I don't see how you can have both as the splines are different lengths.
I hope that helps, please let me know if you have any further questions.