Need to top off pumps for Drive Trim and K-Planes and was wandering what fluid to use ? Should I use Mercury Power Steering and Trim Fluid in both ?

most of the later model trim pumps use 10 w 30.

How about changing all the fluid in the reservoirs and using Mobil 1 10 W 30 synthetic for both trim and tabs ?

I would try to use a different color oil for each application. You can trace a leak much easier that way.