paralleling followers of different types

Rather than patching in a parallel circuit why don't you simply replace the exiting curcuit with one that has the ratings to meet your drive requirements. This way you can eliminate the questions of how paralleling will work or not work.

When you go to make this change do note that you will have to carefully consider the voltage levels and biasing characteristics of the source that drives the follower. If you end up replacing a BJT follower with a Darlington combination to get more gain there is an additional B-E junction drop to consider. On the other hand if you decide to create a MOSFET follower note that the threshold voltage range of the FET will likely be in a range of volts instead of the single Vbe of the BJT circuit.