Consistency is what is important.  If you read with one, read with all.  If there's no one to read with someone and it's the only person who you would read with, have another production staff member do it.  It is far better to have everyone audition with random readers than to have a few audition with someone reading the part exactly as you want it.

I'm with KEB - as the Director you should NOT read with the auditioning actors.

The Director's job is to watch and to listen to the actors; and it is difficult (?impossible?) to do that job if you're reading along with them.

Get someone else to read with the auditioning actor.  Anyone.  If not a production team member, then another actor (someone else auditioning, or someone you bring along with you just for the express purpose of reading).