That is a little different.
In this case AFAIK he can be convicted on any of the charges not dependent on the other charges.
Right, because he has to show that in each case his claim of self defense (which includes several factors) is valid. Even if he is acquitted on the charge of killing Rosenbaum, he still would have to prove (or at least introduce reasonable doubt) that he had all of the factors of self defense in killing Huber.
For example, if he did not have a reasonable fear that Huber was going to kill/severely injure him, then he has no claim to self defense in killing him, regardless of what happened with Rosenbaum.
However, showing that he was acting in self defense in the Rosenbaum shooting does support the "Innocence" factor of his later self defense claims