I would suggest that it is better to get the shot right when the shutter button is pressed, rather than rely on PP to rectify any shortcomings.
I suspect camera shake is at least a contributory factor, due to nothing in any of the pictures being sharp (in focus), and suggest checking that you are holding the camera correctly. With a total reach equivalent to about 630mm, assuming hand held, this would magnify any shake. A heavy crop (assuming you shot at max. resolution of 12MP) down to the 300 odd KB will only enhance any shortcomings of the shots.
Try getting closer (move slowly, or even wait and see whether the bird will come towards you). I tried a pied wagtail the other day with a Fuji HS20 (720mm reach), just could not get close enough, once cropped worse than yours and promptly binned.
For added support, try a monopod - easier to carry and set up. You can have it attatched to your camera or lens retracted and set up in seconds. no issue you sometimes get with a tripod in a crowd
As mentioned, I don't know what teleconverter you are using, take it from someone who has tried and only proved that to get the reach and the quality you'll have to spend money on decent glass