RE: Offrir des fleurs aux vendeuses?
If you are to use pronouns for every noun in the question, then you will need to replace "some flowers" (des fleurs) with a pronoun also, will you not?
--The Question Here is what you have written: Tu leur as offris at fleurs?
1. If you are making this sentence in the past and using Passé. Composé, the past participle of offrir is offert, not offris.
2. des fleurs (some flowers) is an indefinite article with a noun, so should this not be changed also? The pronoun to replace des fleurs with is en. Whenever en (meaning "some") is used with another object pronoun, it always comes in the second position.
**So, this gives you the following sentence: Tu leur en as offert? (Did you offer them some?)
--The Answer Here is what you have written: "Non, ne me l'offris pas am fleurs
If the question is "Did you offer them some?" Then the answer in the negative should read "No, I did not offer them any." (Passé Composé of "I offered"=J'ai offert; to them=leur; any=en)
**So, this is the sentence you want: Non, je ne leur en ai pas offert.(No, I did not offer them any.)