These are certainly non-rigorous answers:

(1) The Apprentice: it's sized for a 15 motor, so your G25 should have plenty of power. The G25 is spec'd for a burst current of 44A, so they specify a 50A ESC. The actual amps you pull will depend on your style of flying, prop size, the amps the motor draws, the amps the battery delivers, but I'd guess that cruising around in mid-air the Apprentice probably draws 10-15 amps. So it should work, but the motor probably won't be working at its best efficiency. You may also have to check the CG, as I'd bet the G25 is heavier than the stock motor.

Where you might run into problems is full throttle operations, where the motor might pull more than 30 amps. That could burn out the 30A ESC, although it probably will tolerate short bursts of high amperage. If you fly it in a conservative manner, you'll probably be OK. If you're gonna put on a larger prop and fly 3D, you could run into problems.

(2) The T-28: Parkzone says it comes with a 480 size 860Kv motor. You could just go down to the LHS and get an eFlite 480 to replace that. If you're going to go the HK route on this, there's a Turnigy 480 size 1020Kv motor that will probably work. Or if you want to try to spice things up, get an eFlite Power 10. I did that in my mini-Showtime, which is spec'd for a 480, and love it.

In both cases, I doubt that these motors will be a direct replacement for the existing set up, so you'll have to figure out how to mount them on the supplied mounts, or come up with some kind of substitute system.

Hope this helps.