I found this on :
http://www.namdrah.net/cdd/CDDMirror/filmmakers.html
Look at this extract :
"In 1992 Ruby and Lesser sold the animated feature "Balto" to Amblin Entertainment."
Does this mean that the main idea and story of Balto was brought first by them, the two writers who worked on Balto 3? In that case, it's really great because they are the only ones from the original who worked on one of the sequels...

And since they are still working for Universal and making stories for DTV sequels, it seems like they will be there for the next sequels.