Omitting auxiliary verb when subjects are different

I am curious whether it is possible to omit the latter same auxiliary verb in the sentences linked with conjunction, even if the subjects are different.

For example, are they both possible to write "We shall do it, and they shall follow him" and "We shall do it, and they follow him" for the same meaning?

If we change this a little into a similar sentence like "We shall do it, and he shall follow it", and "We shall do it, and he follow it", we can easily notice that it is not "he follows it", and "shall" is omitted.

But coming back to the original sentence "We shall do it, and they follow him", is it possible to infer that "shall" is omitted in the later part of the sentence just like "We shall do it, and they shall follow him"?

Please give me intellectual help about this question in terms of grammatical possibility, not of practical desirablity. I am basically asking a theoretical question.

Thank you!