I have just re-checked adding any of those functions and the node is working correctly without missing function error.
Does the “missing function” node appears immediately as soon as you add any of these functions, or at some later point?
Also, what OS are you using, what Unity version and what target platform is set in build settings? So that I can double check those specifically.
These are part of the free DOTween version so everything should work fine. Are there any console errors or warning at all by the way? For example, if you are using NodeCanvas, it already includes a version of DOTween within. If you have manually imported DOTween a second time this might create a duplicate and thus possibly and error, but the console should inform you if so. Can you please confirm?
Finally, may I suggest that you use the DOTWeen extensions from the Downloads section of this website until I figure out what the problem is?