Does anyone have any substantiation that the translations are not correct?
No. The translations probably are pretty accurate.
Can anyone provide independently derived confirmation that Memri (or whoever) falsified the "cartoon or translation"?
Falsified, I doubt it.
Do we have independent analysis that memri is not objective (or at least no more than the people who put the cartoon together)?
I think it's fair to say Memri are about as objective as Iranian state TV

So far in reading the thread I see alegations of falsification of translations, out right fabrication of the cartoon but nothing to substantiate the allegation. An allegation is not proof or evidence of anything. If you have something to substantiate it please provide it, and that goes for either side of this argument. FWIW the "translation" certainly seems to follow the graphical plot line. I'm not sure what esle could be added to it to change it to a different meaning
Well, the plot of the cartoon is Israeli soldier kills family, boy swears vengance, boy participates in attack on Israeli military convoy, boy carries out a suicide attack on convoy.
The ending shows all the attackers and Israeli soldiers dead, with one surviving boy who walks off into the sunset. With no celebration or victory signs, it's actually close to a traditional anti-war film. Especially as the main target, the evil Israeli officer, isn't seen being killed, and his body isn't one of those shown after the battle (as far as I can see)
What we don't get with Memri is context, and we don't see any scenes they might have edited out.
What I'd really like to see for comparison is an Arab version of Memri, where they paint the West and Israel as evil based on translations of Pat Robertson, Ovaida Yosef, Jean Marie le Pen, etc. Throw in bits of Hollywood films (Black Hawk Down would be a good place to start) and you'd end up with a convincing portrayal of a west that hates anyone who isn't a white Christian,or Jew and hell bent on killing as many Muslims as possible.
It wouldn't be accurate, of course, but you can achieve a lot by presenting only one side of a story (when the other side isn't around to present their side)