From the look of the screen shot it looks like you have spatial analyst so you could use this approach:
- Convert polygons to rasters.
- Run the rasters through the Thin tool.
- Convert raster skeleton back into a polyline dataset.
- Edit as necessary.
You will need to experiment with thin options and certainly do some post thinning editing of the vector lines to remove the spurs\loops that will be generated. As you have a few polygons to deal with then the editing time will be fairly quick. Below is an image of the output of a Thin tool before its converted to a vector line for editing ran on some polygons I have.
If editing sounds too much you could turn the polylines into a network dataset and extract out routes between 2 points which would be the centreline. Just an idea?