Moving wordpress: redirect best practices?

Hello Friends
I will merge 2 blogs located in subdomains. Both are the same blog but in different languages:
englishblog.domain.com
spanishblog.domain.com

I'm going to merge them in domain.com/blog (I'll use wpml to handle the translation) bit I'd like to know your opinion on how to handle the redirections.

The easy way is to send everything to the new domains. But I'd like to send each post to it's new location:

englishblog.domain.com/postx
spanishblog.domain.com/postx

go to
domain.com/blog/postxenglish
domain.com/blog/postxspanish

This is because I want to keep the ranking of the blog.
Is there any tool to do such thing? And what do you think about it. Is it worth going trough this details?

Thanks!!