I claim no expertise in tandem kayaking, but consistent with accepted Internet Policy and Practices, I won't let that stop me from giving advice.
For someone just starting out, wanting to be competent but not necessarily get fancy, how hard can it be? Don't wait, do what they are already doing, get out, paddle, experiment...
Take standard Tandem canoe practice skill sets and strokes.
Stern paddler:
Forget the "J" stroke, why do that when you have the option of a forward power stroke or sweep on the opposite side? Besides, without a "T" grip, a J stroke is going to awkward to near impossible anyway.
Pry strokes - less often. generally a draw on the opposite side will achieve the same end goal with less chance of "tripping" over the paddle in shallow water.
Bow paddler:
Forget "crossover" strokes like the cross-bow draw. Again, no longer needed, potentially awkward...
General:
Person with more tandem knowledge should probably be in the stern so they can see what the partner is doing and call for specific strokes when needed (note, "knowledge" may be different than "experience" - knowing what you are doing and why, vs time just spent in a boat with another partner...)
Be sure to check the "trim" - if the boat is bow-heavy, then it will be more difficult to keep it going in a straight line.
This does NOT mean the heaviest person needs to sit in the back, unless you are extremely mis-matched like 250# and 120#, for example. Just adjust where you put any gear - if the heavier person is up front, then slide both seats further back, and put ANY and ALL gear you have behind the back seat, not somewhere in middle of boat.
Bottom line, I think anyone who could help with tandem canoeing tips could also help give beginning tandem kayaking tips.
I do have a tandem canoe though to use every great once in awhile