To create a Multi Row Slider, you just need to provide number of rows in the Rows field. Make sure Slides Per Row is set to 1, and then finally you can use the Number of Columns fields to provide number of posts for each row separately for each device.
- Advanced -> Rows : 2
- Advanced -> Slides Per Row : 1
- Slider -> Number of Columns : Any
Other settings can be setup as per your need.