Same series different numbering

[Costanza]

Hi, long time Librarian, newly dumb evidently, needing help!

Like many series, when translated in Italian they split one book into two different parts.
I was trying to either put them all under the same original series (in this case Publio Cornelio Escipión by Santiago Posteguillo) or into a new one (Publio Cornelio Scipione) dedicated only to the italian version (as suggested) but I made a mess, also by adding them to a series from the book edit page.
So, first of all, what would you suggest? Keeping them in the original one or is it better to create a new one?
Second. How can I delete the series from the book once I've decided in which series to put them? Is there someone with higher clearance then me? Because I can't find a way to do it...
Third. How do you combine the two different series? They are ultimately the same series...

Anyway the books are:

https://www.goodreads.com/book/show/2... #1 (italian and spanish)
https://www.goodreads.com/book/show/2... #2 (italian and spanish)
https://www.goodreads.com/book/show/4... #3 (italian and 1/2 of the spanish)
https://www.goodreads.com/book/show/4... #4 (italian)

Thanks to anyone who will help, either by doing it or by telling me how to do it so that next time I won't mess up!

[Renske]

There are no strict rules if a series needs a separate series for the split editions. For me the number of books in the series matters.

Removing a book from a series is done from the edit page of a series.
Series pages can't be combined/merged, only deleted.