You want to look at the die level detail. Two sources could be two
ends of a fat slab, or one could be "for drain current" and the other
"for gate driver Kelvin ground" with very different current capacities.
Since you are not actually using a gate driver I would say to just
tie them both to the output.
Now when you say "amplifier" I see a "source follower" which will
sure boost available output current, but not very linearly or at all
controlled (other than by what the load wants to take, at the
delivered output voltage).