Edit based on Joao's comment*
The domains in question are cctld, i.e .es, .it, .pt. Geotargeted subfolders on country specific domains don't work well, if the top level domain is generic (i.e. .com) this solution works. Otherwise, from a pure "best for ranking" perspective, keeping cctlds that only serve one country is best, but, like every solution, each has it's drawbacks such as additional technical overhead and having to market/optimize each cctld independently rather than consolidating signals to one domain (subfolder approach).
Great question, I don't fully understand your setup but I think this should describe it and how to deal with it:
exemple.com/index_en.html === exemplo.com/index_en.html &&
exemple.com/index_es.html === exemplo.com/index_es.html
Your 3rd option is best, use 301 redirects to redirect all pages from exemplo.com to exemple.com on a 1:1 basis, i.e. redirect each page to its equivalent. You should determine which domain is the preferred domain by checking which one ranks better/gains more traffic (the preferred domain should also have higher external link count and links from decent websites)
The preferred domain in this hypothetical scenario will be exemple.com. When a request originating from a UK IP to exemple.com, you will 302 redirect them to exemple.com/index_en.html.
A request originating from Spain with a Spanish IP to exemple.com should 302 to exemple.com/index_es.html.
That would be it - don't redirect any other requests on the domain, use hreflang to annotate the spanish and english versions accordingly.
I did the Redbull.com setup and a friend of mine did theguardian.com. We followed Google engineer's advice despite doubting the 302 redirect. The hreflang lead, Christopher Semturs confirmed in a comment on a post I wrote here.
I would highly advise you take precaution when consolidating your domains (vigoriously check google search console, run crawls, etc..) and test the international configuration (be ready to roll back immediately) as well.