That "sleep slowly" phrase makes me think the original Japanese line might be a yukkuri shiteitte ne reference.

Why all the english sentences were translated?
Were they grammatically wrong or something?

Less a question of grammar than of vocabulary: the wording used was stilted and unnatural, so the translations were added to make the meaning clearer.

Isn't 4 Flandre a spell card thing?

Yes I believe that is her 'Four of a Kind' spellcard

I'm still not sure about Remilia as Charlie Brown, but Flandre as Sally... works.