Hey,
Use CSS to float the input widgets left and right and clear the float before adding a new row in the tab panel.
For example,
# Row 1
div("style: "float=left;width=33.33%;",SselectInput(.......))
div("style: "float=left;width=33.33%;",SselectInput(.......))
div("style: "float=left;width=33.33%;",SselectInput(.......))
#Row 2
div("style: "clear: both;",numericInput( ......))