If you mean a literal “&”, none of the proposed forms is meaningful. In an informal communication, you'd use the first name followed, if necessary, by e famiglia. For instance:
(Saluti da) Mario e famiglia.
In a formal context, you might use famiglia followed by the family name:
(Sentite condoglianze), famiglia Rossi.
Probably neither. Since in Italian whoever as a laurea (the lowest universitary degree) is entitled to be called dottore, or dottoressa for a female, chances are that whoever holds a high-level post in a firm or other organisation has this title. So to be on the safe, you may use dott. for a male and dott.ssa (or dott.) for a female.
As for signora / ...
A generic common courtesy phrase that could be added as conclusion could be
"La ringrazio per la cortese attenzione."
In this specific case I think I would write:
"La ringrazio per la cortese attenzione nei riguardi della mia
According to this page a formal salutation could be
Reverendo Padre Rossi
is slightly less formal.
Also according to the same page, the letter should end with a phrase like
La prego di accogliere, Reverendo Canonico (NAME AND SURNAME) l'espressione dei miei sentimenti deferenti
(YOUR NAME AND SURNAME)
In my experience, the most common solution is avoiding the problem by using a different salutation (for instance, just buongiorno) or switching to a first-name basis earlier than normal practice would suggest (in particular, gentile Anna would sound perfectly OK between coworkers in a firm with a relaxed culture).
I don't tend to 'doctor' people I don't know,...
You can find on Treccani's appellativi e epiteti [prontuario] a list of proper forms for most of ecclesiastics and their abbravistions.
For a bishop:
(Sua) Eccellenza (S. Ecc. o Sua Ecc.): vescovo o alto prelato; nella
tradizione, prefetti e questori, e così via;
for a cardinal:
(Sua) Eminenza (S.E. o S. Em.), Eminentissimo (Em.mo, E.mo):