The problem here is not prepositions, but parallel structure. An English sentence can have any number of verb phrases in the predicate, but they all have to be in the same tense, etc. Likewise, a sentence can have as many noun phrases as you want in the subject, but they all have to be the same type of noun phrase i.e. infinitive or gerund.
1) Sentence a) should be changed to: fighting...believing...and doing are much more important than having.
Sentence b) is correct as written. The to before fight is not a preposition, it is making fight an infinitive, and can also serve to put believe and do into the infinitive form.
2) Confuse with in that context sounds fine to me.