How to add two colour legends to a plot?

I have two overlayed plots.
Two related questions:

  1. I would like to be able to show the colour legend for each (it is currently only showing one)
  2. and not as essential, I would also like to be able to set the colours to specific colours for specific values (similar to scale_fill_manual in ggplot)

The plot looks like this:

And the code portion:

plot_ly(data = WBasel,
              x = ~factor(Station_No),  #to add salinity data
              y = ~-Depth_Sample, 
              color= ~Salinity,
              type = 'scatter',
              mode = 'markers', 
              size = 8, 
              showlegend = FALSE) %>% 
    add_trace(x = ~factor(Station_No),  #to add temperature contours
              y = ~-Depth_Sample,
              type = "contour", 
              showlegend = FALSE

Thank you.