For the 17 month old, my only suggestion would be to catch him before he throws it… which means being on top of him from the second you think he's starting to fill up, then grabbing it before he decides to throw (or as he's throwing it), and guide it down (to the table if he has a tray or further away from him if he's at the table). Then praise him "good job not throwing your food! I'm so happy you decided to put that on the table instead. You can say 'all done' and I'll take it away." Throwing when they're done is trickier because if you take it away after they throw it, that's pretty much what they were going for. All you can do is make him use the appropriate action and then praise praise praise so that becomes the most desirable option.
The other one I would explain in simple language "don't push, say 'more.'" Initially i think you might have to deal with the pushing, but don't give him anything until he says more. It's a simple enough word that he can mimic or at least make an attempt. Once he's got that down you can work on the pushing. I'd give a lot of warnings throughout the meal 'remember, don't push, say 'more.'" If nothing, I'd start getting tough on him: if you push, your plate goes away and you're done. If he understands everything, he should be able to get it, it's just easier for him to shove his plate away than practice new language. How long has he been with you?