Having them all in a line has worked well. Possibly that bright reflection of the hind leg at the far right side is a little distracting. But nothing to worry about.
Looks fine at the displayed size but is somewhat soft in the bigger version.
Try a bit of contrast adjustment on just that front one and see if that improves it or not.
Perhaps cropping out the brown vegetation in the left corner right before the little turtle,I like the image btw
I think it is a very nice shot , dave. And the sharpness is perfectly acceptable.
The short answer is ISO 1250 and f/11, and focus on the second turtle from the left. (use a tripod if you have one handy)
Nice shot, Dave. I would tone down that bright reflection that Geoff pointed out.