Day of the Dove" would seem to make it clear that one transporter console can beam up at least nine people simultaneously
In The Apple perhaps the transporter could have dematerialize the first six and held them, then dematerialized the additional three, and rematerialized all nine at the same time?
Using this method, the Enterprise with only a single six pad transporter could materialize a hundred "Starfleet Marines" on a planet's surface all at the same time.
It would depend on how much power was available and the number of clear transporter frequencies. I think the TOS-E had multiple transporter rooms but only one was active at a time. If all were active, they could be all used to do a "tactical" aka fast beam down.