You shouldn't have talked to the manager and your brother shouldn't either.

[navi tasan]

Can one use #1 instead of #2?

1) You shouldn't have talked to the manager and your brother shouldn't either.
2) You shouldn't have talked to the manager and your brother shouldn't have either.

Can one use #3 instead of #4?

3) You shouldn't have talked to the manager and neither should your brother.
4) You shouldn't have talked to the manager and neither should your brother have.

 

[emsr2d2]

Can one use #1 instead of #2?

1) You shouldn't have talked to the manager and your brother shouldn't either.
2) You shouldn't have talked to the manager and your brother shouldn't have either.

They're both grammatically correct but they're not interchangeable.
#1 makes it sound as if you're advising that "your brother" shouldn't speak to the manager in the future.
#2 makes it clear that both people spoke to the manager and that the speaker thinks that was a bad idea.

Can one use #3 instead of #4?

3) You shouldn't have talked to the manager and neither should your brother.
4) You shouldn't have talked to the manager and neither should your brother have.

#3 has the same meaning as #1.
#4 isn't grammatically correct. If you want to express that both people talked to the manager and it was a bad idea, use "Neither you nor your brother should have talked to the manager".